Summary: Add debug-gated QUIC lifecycle snapshots to distinguish stale-connection recovery from general request slowness. Requests now record connection age, last RX/TX age, signed idle-deadline distance, and timer counts at request start and completion. mvfst reports separate idle and keepalive callbacks plus overdue-deadline observations; ngtcp2 reports its unified transport timer. Recreated requests preserve the prior connection UUID so the request can be joined to the close reason and replacement connection.
Reviewed By: jbeshay
Differential Revision: D125287129
fbshipit-source-id: 921046a7ed2a6273fde59be0125dcbd8904ccaf4