GH-50398/GH-50829 2/6: Remove pyarrow.benchmark and simplify parse helpers

[fboudra]

Rationale for this change

#50398
#50829

What changes are included in this PR?

Two unrelated small cleanups.

The first part removes the internal benchmark module: pyarrow/benchmark.py, pyarrow/benchmark.pxi, benchmarks/microbenchmarks.py, src/arrow/python/benchmark.{cc,h}, and the CMake registration. Nothing in the tree imports it, and it is not needed for the limited API work, so it goes.

The second part is three simplifications in the parse helpers:

• helpers.cc gains PyBytes_AsStdStringView so the repeated bytes/UUID-to-string-view code has one place to live (this also addresses review comments on the helpers)
• ParseBinary uses ARROW_DCHECK(!PyErr_Occurred()) instead of RETURN_IF_PYERROR after the PyBytes/PyByteArray accessors, which cannot fail on an object that already passed the type check
• ParseUuid drops a redundant RETURN_IF_PYERROR

Deletions and call-site simplifications only. No behavior change; the test suite stays green.

Are these changes tested?

Yes

Are there any user-facing changes?

No

Was AI used for this PR?

PR code and description written by:

• [x ] Human
• AI

Reviewed before submission by:

• [ x] Human
• AI
• Not reviewed

• GitHub Issue: [Python][Packaging] Support abi3 wheels for pyarrow #50398

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