feat: add advanced cache/batch features, expand hard test coverage, and 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.

Author: Rahulcse79

.gitignore

@@ -28,6 +28,21 @@ dist/
 
 # python testing things etc
 .coverage
+coverage.xml
+htmlcov/
+.pytest_cache/
+.ruff_cache/
+.mypy_cache/
+.tox/
+.nox/
+
+# packaging
+*.egg-info/
+__pycache__/
+
+# editors
+.vscode/
+.idea/
 .nox
 env
 googlemaps.egg-info