x.encoding.asn1: another minor cleanup

[blackshirt]

This PR is rather of
follow-up from previous PR in attempt to improves x.encoding.asn1 module, as availables in 22948, 22932, 22861, and 22847 PRs.
This PR contains some small changes to the module:

• Refinement to align with the latest fix of Option unwrapping. (mostly from @felipensp, thank guys)
• Just removes .str() from sequence and set for now, its needed to allow just dump current sequence fields.
• Unifies some of RawElement methods
• Some small refinements.

The latest bench run with -prod flag results in

Benchmarking ASN.1 encode...
Average example encode time: 1 µs
Benchmarking ASN.1 decode (with asn1.decode)...
Average (asn1.decode) decode time: 1 µs
Benchmarking ASN.1 decode with Example.decode)...
Average (Example.decode) decode time: 1 µs

Its likely on par with the go version bench availables on bench dir. The previous patch help reduces some overhead of it.

_{Huly®: V_0.6-21409}

[spytheman]

Excellent work.
Less code, more performance 🥳 !