ci(build): build several pull requests together

[adriadam10]

What

The pr input of the Build dispatch takes up to 8 pull request numbers, separated by spaces or commas. They are merged into main one after another and built and tested together, so a batch of reviewed pull requests needs one Windows run instead of one each. A single number works as before.

• eligibility checks every pull request, takes the union of their files for the relinker, register context and write watch decisions, and logs one PR #N at <head> merged into main at <sha> line per pull request.
• The merge steps of relinker, linux and windows merge the list in order; a stale head or a pull request that does not merge on top of the previous ones fails with its number.

Tested

Linux: actionlint clean. The merge step run as is on main 145cb82 with #4593 and #4783 merges both; a stale head fails naming the pull request. The eligibility script run under node against the live API: a two-PR list gives the expected outputs and lines; a closed PR, a malformed list and 9 numbers are rejected.

Checklist

• Based on current main; no other open PR implements the same functions
• One topic per PR; follow-ups go in a new PR
• No comments in code except technical debt
• Unimplemented paths throw (NotImplemented_nid_no_patch); silent stubs are listed under Silent stubs in their library's technical debt file
• No notes, investigation .md files or images added to the repository (attach them to this PR)
• New third-party code is a submodule built from source
• Generic behaviour, not specific to one title
• Depends on: none
• Unblocks: none
• GPUs tested: n/a
• AI-assisted: yes