PYTHON-4204 Optimize JSON decoding using lookup table to find $ keys

[ShaneHarvey]

PYTHON-4204 Optimize JSON decoding using lookup table to find $ keys.

This change improves JSON decoding by 20-50%+:

https://spruce.mongodb.com/task/mongo_python_driver_perf_tests_perf_6.0_standalone_patch_698599c737925ccac5c27cc58bb48b2692c74e30_65c2ad625623431a4f5596c5_24_02_06_22_06_33/trend-charts?execution=0&sortBy=STATUS&sortDir=ASC

I also tested set intersection but the for-loop approach performs better:

def object_hook(dct: Mapping[str, Any], json_options: JSONOptions = DEFAULT_JSON_OPTIONS) -> Any:
    matches = set(dct) & _PARSERS_SET
    if matches:
        return _PARSERS[matches.pop()](dct, json_options)
    return dct

[ShaneHarvey]

This lets us see the print()s in the pytest output:

 [2024/02/06 14:45:55.785] + python -m pytest -v --capture=tee-sys --durations=5 --maxfail=10 test/performance/perf_test.py
 [2024/02/06 14:45:56.173] ============================= test session starts ==============================
 [2024/02/06 14:45:56.173] platform linux -- Python 3.10.4, pytest-8.0.0, pluggy-1.4.0 -- /data/mci/6a62d81f9a459de6454c8a15a2244eb2/src/.tox/test-eg/bin/python
 [2024/02/06 14:45:56.173] cachedir: .tox/test-eg/.pytest_cache
 [2024/02/06 14:45:56.173] rootdir: /data/mci/6a62d81f9a459de6454c8a15a2244eb2/src
 [2024/02/06 14:45:56.173] configfile: pyproject.toml
 [2024/02/06 14:45:56.335] collecting ... collected 25 items
 [2024/02/06 14:45:56.442] test/performance/perf_test.py::TestFlatEncoding::runTest Completed TestFlatEncoding 330.739 MB/s, MEDIAN=0.018s, total time=0.183s
 [2024/02/06 14:45:56.666] PASSED          [  4%]
 [2024/02/06 14:45:56.666] test/performance/perf_test.py::TestFlatDecoding::runTest Completed TestFlatDecoding 278.886 MB/s, MEDIAN=0.022s, total time=0.217s
 [2024/02/06 14:45:56.833] PASSED          [  8%]

[NoahStapp]

LGTM, thanks Shane!