docx-scalpel 0.1.0a3 — annotation writes + block metadata

Bundles the Python wrapper updates that landed in Docxodus 6.1.0:
- DocxSession.add_annotation / remove_annotation / update_annotation /
  move_annotation (anchor-addressed annotation CRUD)
- DocxSession.get_block_metadata / get_block_metadatas /
  get_list_membership / get_section_info (block-level metadata reads:
  style id+name, outline level, numbering identity, w:sectPr page setup)
- New types: BlockMetadata, ListMembership, SectionInfo, NumberFormat,
  AnnotationUpdate (re-exported from package root)
- fill_placeholders wrapper (mirrors the C# and TypeScript control loop)
- Wire decoders renamed to leading-underscore (_from_wire) — internal

chore(python): bump docx-scalpel to 0.1.0a2

docx-scalpel 0.1.0a1 — first PyPI release