v0.10.1: Multipart text merge compatibility

A multipart-text compatibility fix for the Python library and standalone
Forge Proxy.

Fixed

• Same-role message merging accepts multipart text content. The
  Llamafile/llama-compatible adapter now extracts text from list content before
  merging, avoiding a TypeError in affected Proxy requests, including those
  using reasoning replay. Plain-string formatting and existing merge rules are
  unchanged; nonmerged messages retain their original shape. Merged content is
  text-only and does not preserve non-text blocks or block-level metadata.
  Fixes #151 via #163; thanks to @xh123637.
• Standalone Forge Proxy bundles include the same multipart-text merge fix.