perf: improve JSON signature regex for performance and clarity

[mancuoj]

Changed capturing groups to non-capturing groups in JsonSigRx regex to slightly improve performance, as captured groups were not being used.

[pi0]

Thanks for PR but can you please also share a benchmark diff report against both Node.js and Bun? 🙏🏼

(since this is a security area, i rather to minimize changes and only make it if it really makes a change)