Add an e2e suite covering go-gost/x#125: a malformed UDP datagram sent
to a cipherKey-enabled QUIC listener must not close the shared transport.
Uses the canonical http-over-quic chaining pattern and verifies the
forward still works after the invalid datagram.
Also bumps go.mod/go.sum (plugin v0.6.1, otel, x/net, etc.).
