Handle closed QUIC handshakes gracefully

[lukaszsamson]

Avoid crashing QUIC acceptors when a client disconnects during handshake and add an HTTP/3 regression test reproducing the close-during-handshake path.

Before the patch test fails with:

=case          rfc9114_SUITE:handshake_close_does_not_crash_acceptor
=logfile       rfc9114_suite.handshake_close_does_not_crash_acceptor.html
=started       2026-02-21 17:03:46
=ended         2026-02-21 17:03:47
=result        failed: {{badmatch,true},
                        [{rfc9114_SUITE,
                             handshake_close_does_not_crash_acceptor,1,
                             [{file,"test/rfc9114_SUITE.erl"},{line,77}]},
                         {test_server,ts_tc,3,
                             [{file,"test_server.erl"},{line,1796}]},
                         {test_server,run_test_case_eval1,6,
                             [{file,"test_server.erl"},{line,1305}]},
                         {test_server,run_test_case_eval,9,
                             [{file,"test_server.erl"},{line,1237}]}]}, [{rfc9114_SUITE,
                                                                          handshake_close_does_not_crash_acceptor,
                                                                          77},
                                                                         {test_server,
                                                                          ts_tc,
                                                                          1796},
                                                                         {test_server,
                                                                          run_test_case_eval1,
                                                                          1305},
                                                                         {test_server,
                                                                          run_test_case_eval,
                                                                          1237}]
=elapsed       0.674052s

Discovered while working on experimental WebTransport for phoenix implementation with cowboy and quicer backend

[essen]

Thanks. I will take this into account when redoing the listener/handshake part properly.