[core] Load plugins on demand (#11305)

- Adds `--no-plugin-dirs` to disable plugin loading
- `--plugin-dirs` now supports post-processors

Authored by: coletdjnz, Grub4K, pukkandan

pyproject.toml

@@ -384,6 +384,7 @@ select = [
     "W391",
     "W504",
 ]
+exclude = "*/extractor/lazy_extractors.py,*venv*,*/test/testdata/sigs/player-*.js,.idea,.vscode"
 
 [tool.pytest.ini_options]
 addopts = "-ra -v --strict-markers"