Rebase refactoring on GA API branch (PR #175)

- Reset branch to users/sagebree/api_alignment_client_server tip
- Re-apply base class extraction: _ODataBase, _BatchBase, _QueryBuilderBase
- Re-export multipart helpers from _batch.py for new PR #175 tests
- Update test_sql_parse.py patch target: urlparse now in _odata_base
- All 1658 tests passing

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Abel Milash