fix(json_schema): keep pattern alternations inside JSON quotes

[original4422]

Summary

JSON Schema string patterns with a top-level alternation were interpolated directly between JSON quote characters. That allowed the alternation to bind across the quotes, rejecting valid values while accepting malformed JSON.

This change wraps the interpolated pattern in a non-capturing group inside the quotes. It preserves user capture numbering while keeping every alternative within the JSON string. The regression test covers unanchored and paired-anchor alternations, malformed missing-quote inputs, a simple pattern, and an already-parenthesized pattern.

Fixes #267

Validation

• cargo test string_pattern_alternations_stay_inside_json_quotes -- --nocapture
• cargo test json_schema -- --nocapture
• cargo test
• cargo fmt -- --check
• cargo clippy --all-targets --features python-bindings -- -D warnings
• Python 3.14: maturin develop
• Python 3.14: pytest tests/test_json_schema.py tests/test_imports.py -vv (10 passed)
• Direct Python full-match reproduction accepts both valid alternatives and rejects both malformed missing-quote inputs

pre-commit run --all-files passed every hook except cargo-fmt, which could not start because this host uses Homebrew Cargo without rustup and therefore cannot resolve cargo +nightly. The equivalent stable cargo fmt -- --check passed; the changed code does not involve the repository formatting options that are nightly-only.

Checklist

• The title describes the change.
• A high-level description and the relevant issue are included.
• The branch is based on the latest main commit.
• The change is one logical commit and follows current naming conventions.
• Tests cover the regression.
• No documentation update is needed because the public API is unchanged.

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[original4422]

Hi @RobinPicard, when you have a chance, could you please review this PR and let me know if any changes are needed? Thanks!