Fix HTTP/3 dialtesting timing collection and traceroute IP selection.

[zhengb-gc]

Changes

• Add HTTP/3-specific timing collection for DNS, QUIC connection, QUIC/TLS, TTFB, download, dest IP, and cert fields.
• Rebuild HTTP/3 transport per Run() so reused QUIC connections do not leave response_dns, response_connection, and response_ssl as 0.
• Clear stale destIP between runs and close HTTP/3 transports on reset/stop.
• Keep HTTP/1.1 and HTTP/2 behavior unchanged.
• Make TCP/ICMP traceroute reuse the selected dial IP instead of resolving independently.
• Prefer IPv4 when DNS returns both IPv4 and IPv6.
• Increase default traceroute timeout/retry values to reduce false failures on slower paths.
• Add test hooks for DNS lookup and traceroute execution.

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