gh-113367: Avoid redundant gotos and labels in Argument Clinic

[Prateek99-s]

Summary

When an Argument Clinic function has optional positional arguments and optional keyword-only arguments without any required keyword-only arguments, clinic generated gotos to `skip_optional_pos:`, which immediately performed a redundant check and second jump `if (!noptargs) goto skip_optional_kwonly;`.

### Changes
1. Tools/clinic/libclinic/parse_args.py:
   - If there are no required keyword-only arguments (`not self.min_kw_only`), gotos in the positional section jump directly to `skip_optional_kwonly`.
   - Bypasses the redundant intermediate label `skip_optional_pos:` and the unreachable check `if (!noptargs) goto skip_optional_kwonly;` at the start of the keyword-only section.
   - Preserves separate labels if required keyword-only arguments exist (`self.min_kw_only > 0`).
2. Regenerated clinic headers:
   - Regenerated all affected `.c.h` files via `Tools/clinic/clinic.py --make` (net reduction of ~288 redundant lines across 25 C modules).
3. Tests:
   - Updated golden test file `Lib/test/clinic.test.c`.
   - Verified that all 412 clinic tests pass (`./python -m test test_clinic`), as well as tests for affected modules (`test_datetime`, `test_socket`, `test_bisect`).

[python-cla-bot]

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