Implements the Python SDK with all 9 contract methods, 8 exception
classes, type definitions, asyncio wrappers, and subprocess fallback.
Changes:
- Add Python wrapper module with extract, extract_text, extract_markdown,
extract_stream, search, get_metadata, hash, classify, verify_receipt
- Add exception hierarchy: PdftractError base class with 7 subclasses
- Add dataclass type definitions: Document, Page, Span, Block, Match,
Fingerprint, Classification, Metadata
- Add asyncio module with async wrappers for 4 long-running methods
- Add subprocess fallback for when native module fails to import
- Add conformance test runner under tests/test_conformance.py
- Update pyproject.toml with dynamic version from Cargo
Closes: pdftract-2nu0s
fca8966f45