Remove setuptools from runtime dependency

[ricardoV94]

Drops setuptools as a runtime dependency. It only entered the runtime deps because aesara-devs/aesara#1050 (2022) and #277 (2023) reached for setuptools._distutils.sysconfig and setuptools.errors.CompileError to replace deprecated distutils — stdlib sysconfig had identical equivalents the whole time, and _distutils is a private namespace setuptools makes no stability promises about. The same concern was raised in #2026 but closed without action. Lazy imports in #1170 hid the cost; this PR removes it entirely.

Swaps the four setuptools._distutils.sysconfig calls in link/c/cmodule.py to stdlib sysconfig, replaces setuptools.errors.CompileError with a local Exception subclass, and drops setuptools from [project.dependencies] (kept in [build-system].requires). pytest tests/link/c passes; verified that pytensor.function end-to-end still works with setuptools blocked from import.

Related issues: #2026, #481
Prior PRs: #277, #483, #812, #1170, aesara-devs/aesara#1050