[rtwo2]

Summary

• Upgrade both collector and tests to .NET 10 LTS, and align CI/collection workflows with the .NET 10 SDK.
• Upgrade the collection workflow's GitHub Actions to Node 24-compatible major versions.
• Reject IPv6 unspecified, multicast, and deprecated IPv4-compatible address forms from the public-proxy candidate pool; add regression tests while preserving public IPv6 unicast.
• Make the output validator fail if top_ipv6.txt is missing, while allowing an empty file when no eligible IPv6 candidates exist.

Validation

• The latest full collection on main succeeded: 123,072 collected outputs, top.txt capped at 1,000, top_ipv6.txt generated with 955 entries, 464 generated text files validated, and the Cloudflare/WARP audit passed.
• CI on this PR must pass before merge. Merging this change intentionally triggers one full collection on the upgraded .NET 10 runtime.