PERF: Optimize _categorical_convert CSV parser when categories are known ahead of time

[TomAugspurger]

We should be able to speed up

pandas/pandas/_libs/parsers.pyx

Line 1612 in 2310faa

cdef _categorical_convert(parser_t *parser, int64_t col,

when the users passes a CategoricalDtype.

xref #17643

[jbrockmendel]

Investigating this shows a 4-15% speedup, requires a dedicated cython function. I expect that number would go up if other parts of read_csv get less expensive, e.g. #64515. As is, I'm on the fence as to whether this is worthwhile.

[jbrockmendel]

Investigated in #65018 and decided the perf impact wasn't worth the extra complexity.