Add tests/v3/fuzzer/ with libFuzzer harness covering all four parse
paths (auto-detect, JSON, GLB, float32 mode) with ASan+UBSan.
Fix two bugs found by 10+ hours of fuzzing (~23M iterations):
1. UB: (int64_t)inf in cj_parse_number when extreme exponents like
22222222e222222 produce infinity. Add cj_dbl_to_i64() that clamps
inf/NaN/out-of-range values before casting.
2. Null deref in tg3__parse_string when glTF array elements are not
JSON objects (e.g. "scenes": [[3]]). Add is_object() validation
in TG3__PARSE_ARRAY_SIMPLE and TG3__PARSE_ARRAY_IDX macros.
Verified clean: 5.8M additional runs with zero crashes after fixes.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
