fix(runtime): string.match() honors fancy-regex fallback (date-fns format)

[proggeramlug]

Summary

• date-fns 4.x format() got past constructFrom (PR feat(runtime): .constructor on Date/Array/Object instances #973) but immediately tripped on formatStr.match(/[yYQqMLwIdDecihHKkms]o|(\w)\1*|''|'(''|[^'])+('|$)|./g).map(...) because the regex contains a (\w)\1* backreference. The Rust regex crate rejects backreferences, so get_or_compile_regex substituted a never-match [^\s\S] placeholder and stashed the real pattern in FANCY_CACHE for fancy-regex to handle.
• RegExp.prototype.exec already wired up the fancy fallback (lookup before falling through), but String.prototype.match didn't. formatStr.match(...) therefore returned null, and the chained .map(...) blew up with NULL_PTR_METHOD_CALL.
• Add lookup_fancy_regex(re) helper, have js_string_match consult FANCY_CACHE first. Global flag walks fre.find_iter; non-global returns the full match + capture groups via fre.captures. Pattern + flags + array shape match the standard-regex path exactly.

Validation:

• format(new Date(2024, 0, 15), 'yyyy-MM-dd') → 2024-01-15 (matches Node).
• Also exercised 'HH:mm:ss', 'yyyy-MM-dd HH:mm:ss', 'MMM yyyy', 'EEEE, MMMM do yyyy' — byte-for-byte parity.
• test-files/test_date_fns_format.ts covers the underlying regex shape (global + non-global + no-match) without importing date-fns directly.

Follow-ups (not in this PR): js_string_match_all, js_regexp_test, and js_string_search_regex still consult only the placeholder for fancy patterns. None are on date-fns' format() hot path; the same lookup_fancy_regex helper can be wired in when needed.

Test plan

• cargo build --release -p perry-runtime -p perry-stdlib -p perry
• format(new Date(2024, 0, 15), 'yyyy-MM-dd') returns 2024-01-15 via compilePackages: ["date-fns"]
• Multi-format parity check vs node --experimental-strip-types
• test-files/test_date_fns_format.ts matches Node for (\w)\1* global + non-global + no-match
• CI: lint, cargo-test, parity, compile-smoke, api-docs-drift, security-audit