PYTHON-5395 - Add convert_decimal to CodecOptions #8012

Job	Run time
Typing Tests (3.11)	1m 2s
DocTest	1m 5s
Typing Tests (3.9)	1m 11s
Test using minimum dependencies and supported Python	41s
Link Check	3m 37s
static	4m 44s
CPython pypy-3.10-ubuntu-latest	12m 1s
Docs Checks	27s
CPython 3.13t-ubuntu-latest	11m 13s
Make an sdist	14s
Test async's minimum dependencies and Python	38s
CPython 3.9-ubuntu-latest	11m 10s
Install from SDist and Test	1m 1s
	49m 4s

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