sloproxy

perf(util): introduce `GetGJSONBytesNoCopy` for efficient JSON parsing without data duplication master

- Added `GetGJSONBytesNoCopy` in `internal/util` for safe, no-copy JSON parse operations leveraging `unsafe`. - Replaced `gjson.GetBytes` with the new helper in key payload processing paths (`kimi_executor`, `vertex_payload_helpers`, etc.) to improve performance. - Added unit tests for behavior validation, including edge cases with empty input.