CI fixes: patchelf dev dep for auditwheel, absolute paths in setup.py

- Linux runner lacks patchelf; add the patchelf PyPI package (linux
  only) to dev deps so uv run puts it on PATH for auditwheel repair.
- setup.py anchored all libaegis paths to __file__: newer setuptools
  invoke the compiler from a temp build dir, breaking CWD-relative
  -Ilibaegis/src/include on Windows (C1083 aegis.h not found).

pyproject.toml

@@ -26,6 +26,7 @@ Repository = "https://github.com/LeoVasanko/aegis-python"
 [dependency-groups]
 dev = [
     "auditwheel>=6.8.2",
+    "patchelf>=0.17; sys_platform == 'linux'",
     "pytest>=9.1.1",
     "ruff>=0.16.10",
     "setuptools>=84.0.0",