bytes.fromhex() is 1.3 times slower than binascii.a2b_hex()

Bug report

Bug description:

I was looking at modernising some old code that uses binascii.a2b_hex, and I was surprised to find that bytes.fromhex() is a lot slower:

>>> timeit.timeit('bytes.fromhex("abcd1234abcd1234")', number=10000000)
1.0542256180197
>>> timeit.timeit('binascii.a2b_hex("abcd1234abcd1234")', 'import binascii', number=10000000)
0.4072963949292898

I thought maybe it was a difference in the lookup of the bytes classmethod vs the module lookup. It appears that it is, to some extent, but not completely:

>>> timeit.timeit('fromhex("abcd1234abcd1234")', 'fromhex=bytes.fromhex', number=10000000)
0.6133267850382254
>>> timeit.timeit('a2b_hex("abcd1234abcd1234")', 'from binascii import a2b_hex', number=10000000)
0.3788172130007297

Of course, all these times are extremely small, so it probably does not matter in most situations, but still, I found it surprising.

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Start by reproducing the bytes.fromhex() and binascii.a2b_hex() timeit comparisons shown in the issue on CPython 3.13/Linux, then trace the two named entry points to understand the source of the difference. A useful result would identify whether bytes.fromhex() can be made faster and validate any change with equivalent benchmarks and relevant tests.