feat: add advanced cache/batch features, expand hard test coverage, a…

[Rahulcse79]

…nd refresh README

Added two advanced fork features for production workflows: Pluggable response cache with TTL + LRU behavior, cache stats, and safe key normalization. Concurrent batch executor with ordered results, per-item exception handling, and configurable workers. Integrated cache behavior into client request flow with safe defaults and no breaking API changes. Added large advanced test coverage (including edge cases, concurrency, error paths, and integration-style scenarios) across convert, cache, client, maps, exceptions, and batch functionality. Modernized and stabilized quality gates:
All tests passing.
Lint checks passing.
Rewrote README in a more professional, detailed format: clear feature explanations,
architecture/behavior notes,
usage examples,
development workflow and quality summary.

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Fixes #<issue_number_goes_here> 🦕

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[Rahulcse79]

Thanks for the update. I have completed the CLA and fixed the identity mismatch (commit author email now matches my signed CLA email). The cla/google check is now passing. Please proceed with review when convenient. Thank you.