More various fixes (F-*)

[gasbytes]

bee1900 - expire every peer's session keyparis and staged packets in wolfguard_set_private_key so sessions authnticated under the old static identity do not survive a key rotation.
7ba9799 - hold wg_noise_consume_response key derivation in local buffers and commit chaining_key/hash to the handshake only after the response authenticates
8572893 preserve re-staged packets in wg_packet_send_staged
1ae2f17 - expire consumed cookie after WG_COOKIE_SECRET_MAX_AGE
2065c59 - gate wg_handle_data injection on a full ipv4 header, valid verseion and in-bounds total-length before the alloweddips lookup, closing three source-policy bypasses
962b0c2 - defer igmp query responses to a randomized per-membership timer (RFC 3376, section 5.2) instead of replying synchronously, coalescing query floods into one report per group
51f48f9 - back off dhcp discover/request/renew/rebind retransmissions exponentially by scaling the base timeout by 1<<dhcp_timeout_count up to a 64s cap via a shared dhcp_backoff_delay() helper, instead of retransmitting on a fixed ~2s cadence.
de9ed73 - clamp a peer-advertised tcp mss below the rfc 9293 floor of 536 up to tcp_default_mss in tcp_parse_options so a malicious tiny mss can no longer coerce wolfip into emitting 1-byte segments, and update the two flow tests that negotiated a sub-floor 512 mss to use above-floor values.
056519d - don't emit a forwarding time exceeded for ttl-expired icmp error datagrams this is per rfc 1812 section 4.3.2.7
1056cb7 - deliver a final cb_event_closed through wolfip_poll step 3 when a tcp socket with an armed callback is torn down involuntarily, so close() waiters are no longer starved by close_socket()'s memset.
3a54a3e - set the socket struct (tsocket) callbacks to null in sock_close this applies for both states established and close wait