v0.2.10

• Discarded DATA returns connection flow-control credit. A frame on a
  retired stream, a frame that exceeds the stream receive window, or DATA
  after the peer sent END_STREAM is counted against the connection window
  and answered with WINDOW_UPDATE (RFC 9113 §6.9). A retired stream whose
  frame exceeds the connection window is a FLOW_CONTROL_ERROR. Previously
  the peer's connection send window shrank on every cancelled call and the
  connection could stall.
• One stream-slot predicate (StreamState.occupies_slot) now backs
  open_stream, the server's peer MAX_CONCURRENT_STREAMS check,
  live_stream_count, and retire_stream. The server no longer frees a
  peer stream's slot when only its own side has sent END_STREAM.
• queue_rst_stream marks a known stream reset once the frame is queued.
  Readiness-driven resets now free the slot, and send_rst_stream keeps
  the stream reset when its flush fails with the frame still queued.
• A peer SETTINGS_INITIAL_WINDOW_SIZE change that pushes a stream's send
  window above 2^31 - 1 is now a FLOW_CONTROL_ERROR connection error
  (RFC 9113 §6.9.2). Streams we have reset or finished sending on are
  exempt.
• A request content-length must be one or more digits (RFC 9110 §8.6).
  A non-digit value is a stream PROTOCOL_ERROR. Previously Int() accepted
  signs, whitespace, and digit separators, and -1 matched the
  absent-header sentinel, so the body-length check was skipped.