Add zoptia0regex (Zig regex / RE2 library) to String Processing

[zoptia]

Adds zoptia0regex under String Processing.

It's a regular-expression library for Zig: a faithful port of Go's regexp (Russ Cox's RE2 design) — linear-time / ReDoS-proof, with all three of Go's engines (one-pass, bitstate, Pike VM). It's verified by ~30k differential tests against the real Go regexp (byte-for-byte identical, zero leaks, replayed in CI), and benchmarks ~11% faster than Go on average.

• Apache-2.0, Zig 0.16, build.zig.zon package.
• Entry follows the existing list format.

[gemini-code-assist]

Code Review

This pull request adds the zoptia/zoptia0regex library to the README.md under the string processing section. The reviewer suggests organizing the document by grouping all regular expression libraries under a single section (either "File Format Processing" or "String Processing") to improve consistency and discoverability.

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[gemini-code-assist]

For consistency and better discoverability, it would be highly beneficial to group all regular expression (regex) libraries under the same section.

Currently, other regex libraries in this list (such as tiehuis/zig-regex, shaik-abdul-thouhid/ezi-gex, MahBestBro/regex, and kivikakk/libpcre.zig) are located under the File Format Processing section.

Consider either:

1. Moving this new entry to the File Format Processing section to match the existing libraries.
2. Moving the existing regex libraries from File Format Processing to the String Processing section (which is arguably a more intuitive home for them) along with this new entry.

[zoptia]

Thanks for the catch! I've gone with option 1: moved the entry into File Format Processing, grouped right after the existing regex engines (tiehuis/zig-regex and shaik-abdul-thouhid/ezi-gex), so it's consistent with where the other regex libraries already live.

I kept it to just this entry rather than restructuring others' placements (option 2) to keep the PR minimal — regrouping all the regex libs into a more intuitive home sounds reasonable, but that feels like a maintainer call for a separate change. Happy to follow whatever you prefer.

[jiacai2050]

Agreed, your points are valid and make sense. I will move all those regex libs to string processing later.