Breaking Changes:

• Added Error::InvalidDcidInitialization for invalid custom client destination connection ID initialization, so exhaustive matches on Error need to be updated.

Highlights:

• Added the custom-client-dcid feature, with connect_with_dcid() and connect_with_dcid_and_buffer_factory(), for clients that need to provide the initial destination connection ID. Applications using this feature must satisfy RFC 9000 requirements for destination connection ID unpredictability and length.
• Added C API support for custom client destination connection IDs via quiche_conn_new_with_tls_and_client_dcid() when the custom-client-dcid feature is enabled.
• Fixed retransmission of lost flow-control credit updates, including MAX_DATA, MAX_STREAM_DATA, and MAX_STREAMS_* frames.
• Fixed stream-cancellation retransmission so lost RESET_STREAM frames are retransmitted even after stream collection, and STOP_SENDING frames are retransmitted only while useful.
• Improved stream-limit behavior for long-lived connections by sending MAX_STREAMS updates when available stream credit drops to half of the initial limit.
• Gracefully handles DPLPMTUD probe errors instead of surfacing non-critical send failures.
• Added qlog loss metrics in MetricsUpdated.ex_data, including lost packet and byte totals and deltas.
• Other bug fixes and performance improvements.

Full changelog at 0.25.0...0.26.0