Impl more codecs and _codecs._unregister_error by youknowone · Pull Request #7025 · RustPython/RustPython

- Rewrite _pycodecs.py: escape_decode, charmap_decode,
  unicode_escape_decode/encode, raw_unicode_escape_decode/encode
- Add _codecs._unregister_error with built-in handler protection
  and null byte/surrogate validation
- Normalize encoding name in register_manual
- Add codec error notes via add_note
- Fix cp65001 encoding constant in StandardEncoding::parse
- Remove 35 expectedFailure markers from test_codecs,
  test_pickle, test_datetime, pickletools