Email regex optimization

[nodivbyzero]

Fixes Or Enhances

This PR simplifies the email regular expression, making it more efficient and easier to understand.
Here are benchmarks:

old regex:

Running tool: /opt/homebrew/bin/go test -benchmem -run=^$ -bench ^BenchmarkEmailValidation$ github.com/go-playground/validator/v10

goos: darwin
goarch: arm64
pkg: github.com/go-playground/validator/v10
cpu: Apple M1
BenchmarkEmailValidation/Valid_Emails-8         	  219237	      5463 ns/op	     112 B/op	       7 allocs/op
BenchmarkEmailValidation/Invalid_Emails-8       	  397093	      3025 ns/op	    1193 B/op	      23 allocs/op
BenchmarkEmailValidation/Mixed_Types-8          	 1730408	       693.1 ns/op	     201 B/op	       4 allocs/op
BenchmarkEmailValidation/Valid_test@mail.com-8  	 2442416	       492.8 ns/op	      16 B/op	       1 allocs/op
BenchmarkEmailValidation/Valid_Dörte@Sörensen.example.com-8           	 1768521	       683.2 ns/op	      16 B/op	       1 allocs/op
BenchmarkEmailValidation/Valid_θσερ@εχαμπλε.ψομ-8                     	 1998978	       605.8 ns/op	      16 B/op	       1 allocs/op
BenchmarkEmailValidation/Valid_юзер@екзампл.ком-8                     	 2004871	       600.8 ns/op	      16 B/op	       1 allocs/op
BenchmarkEmailValidation/Valid_उपयोगकर्ता@उदाहरण.कॉम-8                                               	 1836072	       659.0 ns/op	      16 B/op	       1 allocs/op
BenchmarkEmailValidation/Valid_用户@例子.广告-8                                                            	 2668478	       450.8 ns/op	      16 B/op	       1 allocs/op
BenchmarkEmailValidation/Valid_"test_test"@email.com-8                                               	  658518	      1869 ns/op	      16 B/op	       1 allocs/op
BenchmarkEmailValidation/Invalid_mail@domain_with_underscores.org-8                                  	 2313256	       505.2 ns/op	     201 B/op	       4 allocs/op
BenchmarkEmailValidation/Invalid_Empty-8                                                             	 9073566	       131.2 ns/op	     184 B/op	       3 allocs/op
BenchmarkEmailValidation/Invalid_test@email-8                                                        	 2601570	       491.4 ns/op	     201 B/op	       4 allocs/op
BenchmarkEmailValidation/Invalid_test@email.-8                                                       	 2248792	       524.7 ns/op	     201 B/op	       4 allocs/op
BenchmarkEmailValidation/Invalid_@email.com-8                                                        	 5813140	       204.2 ns/op	     202 B/op	       4 allocs/op
BenchmarkEmailValidation/Invalid_"@email.com-8                                                       	  996787	      1127 ns/op	     201 B/op	       4 allocs/op
BenchmarkEmailValidation/Single_Validator-8                                                          	 2536804	       482.1 ns/op	       0 B/op	       0 allocs/op
BenchmarkEmailValidation/New_Validator_Each_Time-8                                                   	   66536	     17918 ns/op	   15404 B/op	     191 allocs/op
PASS
ok  	github.com/go-playground/validator/v10	29.567s

vs. new regex

Running tool: /opt/homebrew/bin/go test -benchmem -run=^$ -bench ^BenchmarkEmailValidation$ github.com/go-playground/validator/v10

goos: darwin
goarch: arm64
pkg: github.com/go-playground/validator/v10
cpu: Apple M1
BenchmarkEmailValidation/Valid_Emails-8         	  325342	      4316 ns/op	     112 B/op	       7 allocs/op
BenchmarkEmailValidation/Invalid_Emails-8       	  545132	      2178 ns/op	    1194 B/op	      23 allocs/op
BenchmarkEmailValidation/Mixed_Types-8          	 1951177	       616.4 ns/op	     201 B/op	       4 allocs/op
BenchmarkEmailValidation/Valid_test@mail.com-8  	 2884880	       417.1 ns/op	      16 B/op	       1 allocs/op
BenchmarkEmailValidation/Valid_Dörte@Sörensen.example.com-8           	 1963050	       608.3 ns/op	      16 B/op	       1 allocs/op
BenchmarkEmailValidation/Valid_θσερ@εχαμπλε.ψομ-8                     	 2448519	       492.3 ns/op	      16 B/op	       1 allocs/op
BenchmarkEmailValidation/Valid_юзер@екзампл.ком-8                     	 2276559	       527.4 ns/op	      16 B/op	       1 allocs/op
BenchmarkEmailValidation/Valid_उपयोगकर्ता@उदाहरण.कॉम-8                                               	 1928568	       643.4 ns/op	      16 B/op	       1 allocs/op
BenchmarkEmailValidation/Valid_用户@例子.广告-8                                                            	 3261272	       374.3 ns/op	      16 B/op	       1 allocs/op
BenchmarkEmailValidation/Valid_"test_test"@email.com-8                                               	 2384032	       508.5 ns/op	      16 B/op	       1 allocs/op
BenchmarkEmailValidation/Invalid_mail@domain_with_underscores.org-8                                  	 2690359	       463.2 ns/op	     201 B/op	       4 allocs/op
BenchmarkEmailValidation/Invalid_Empty-8                                                             	 9082252	       134.2 ns/op	     184 B/op	       3 allocs/op
BenchmarkEmailValidation/Invalid_test@email-8                                                        	 2825318	       419.1 ns/op	     201 B/op	       4 allocs/op
BenchmarkEmailValidation/Invalid_test@email.-8                                                       	 2621067	       459.6 ns/op	     201 B/op	       4 allocs/op
BenchmarkEmailValidation/Invalid_@email.com-8                                                        	 5833818	       205.0 ns/op	     202 B/op	       4 allocs/op
BenchmarkEmailValidation/Invalid_"@email.com-8                                                       	 2549175	       472.6 ns/op	     201 B/op	       4 allocs/op
BenchmarkEmailValidation/Single_Validator-8                                                          	 3027820	       395.4 ns/op	       0 B/op	       0 allocs/op
BenchmarkEmailValidation/New_Validator_Each_Time-8                                                   	   67820	     17648 ns/op	   15404 B/op	     191 allocs/op
PASS
ok  	github.com/go-playground/validator/v10	29.909s

Make sure that you've checked the boxes below before you submit PR:

• Tests exist or have been written that cover this particular change.

@go-playground/validator-maintainers

[coveralls]

coverage: 74.823% (+0.5%) from 74.318%
when pulling 75e6318 on nodivbyzero:email-regexp-optimization
into 6c3307e on go-playground:master.

[deankarn]

I like the simplification and it appears correct, my only FUD is, how confident are we that it functions the same as the previous?

I mean the test still all pass etc.. but wanted to gauge you confidence level as well @nodivbyzero

[nodivbyzero]

@deankarn
I'm pretty confident in this regex. Honestly, I used ChatGPT to optimize the original regex and then tested it with different email addresses.
All tests still pass, so I believe it functions the same as before.