refactor: refactor file filtering for improved efficiency

[mdqst]

I’ve made improvements to the file filtering logic for better performance and readability. Specifically, I replaced the use of .to_string_lossy() with .to_str() where possible, as it’s more efficient when dealing with UTF-8 file names. Additionally, I’ve switched to using Path::extension() for checking .json files, which is a more idiomatic and performant approach.

p.s. This update should help streamline the code.

[codspeed-hq]

CodSpeed Performance Report

Merging #2128 will improve performances by 7.69%

_{Comparing mdqst:patch-1 (37ea977) with main (739ffd3)}

Summary

⚡ 2 improvements
✅ 6 untouched benchmarks

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	analysis	228.3 µs	221.6 µs	+3.03%
⚡	transfer	97.6 µs	90.6 µs	+7.69%

[rakita]

lgtm. fmt pending

[mdqst]

rakita pls merge it