feat(rust): port ci git-refs and ci queue-info to native Rust

[jd]

Adds github_event (GitHub Actions event payload deserialization) and
queue_metadata (MQ YAML fenced-block extraction) shared modules to the
mergify-ci crate, and ports two commands on top of them:

• ci queue-info — prints MQ batch metadata as pretty JSON; errors
  INVALID_STATE (exit 7) outside an MQ context. Appends to
  $GITHUB_OUTPUT with the same ghadelimiter_<uuid> heredoc the
  Python version uses.

• ci git-refs — detects base/head refs from Buildkite env, GitHub
  event payload, refs/notes/mergify/<branch> git notes, MQ PR body,
  or falls back to HEAD^..HEAD. Supports text/shell/json
  output formats, writes base/head to $GITHUB_OUTPUT, and calls
  buildkite-agent meta-data set when BUILDKITE=true.

The notes reader is injected as a trait-object callback so unit tests
can exercise the note-driven detection path without touching a real
git repository; the production path shells out via
real_notes_reader.

The Python implementations of ci git-refs and ci queue-info are
removed in the same PR — the Rust binary now owns both commands
end-to-end. The looks-native heuristic in main.rs learns the two
new subcommand names so argv errors surface as clap exit 2 instead
of silently falling through to the Python shim.

Adds serde_yaml_ng (YAML parser) and uuid (ghadelimiter) deps to
the mergify-ci crate. Binary grows ~100KB to 8.6MB.

19 new Rust tests (8 event/metadata, 3 queue-info, 12 git-refs + 2
format round-trips merged in). Full workspace: 79 tests green,
compat harness 4/4.

Depends-On: #1352

[jd]

This pull request is part of a Mergify stack:

#	Pull Request	Link
1	fix(cli): surface clap's --help instead of erroring on native subcommands	#1380
2	feat(rust): port queue pause and unpause to native Rust	#1352
3	feat(rust): port ci git-refs and ci queue-info to native Rust	#1353	👈
4	feat(rust): port queue status to native Rust	#1359
5	test: derive native queue commands from the binary, not a hardcoded list	#1366

[mergify]

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• depends-on=Mergifyio/mergify-cli#1352 [⛓️ feat(rust): port queue pause and unpause to native Rust #1352 [stack]]
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• depends-on=Mergifyio/mergify-cli#1352 [⛓️ feat(rust): port queue pause and unpause to native Rust #1352 [stack]]
• depends-on=Mergifyio/mergify-cli#1380 [⛓️ fix(cli): surface clap's --help instead of erroring on native subcommands #1380 [stack]]

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[jd]

Revision history

#	Type	Changes	Reason	Date
1	initial	0ca3459		2026-05-05 10:12 UTC
2	rebase	0ca3459 → 9d6db8e		2026-05-05 10:12 UTC
3	rebase	9d6db8e → a2714b7		2026-05-05 10:19 UTC
4	rebase	a2714b7 → 742d92c		2026-05-05 11:16 UTC
5	rebase	742d92c → 839ea5a		2026-05-05 13:13 UTC
6	rebase	839ea5a → 4ddd589		2026-05-05 13:22 UTC
7	rebase	4ddd589 → 3df5705		2026-05-05 15:18 UTC
8	content	3df5705 → 0349b1d		2026-05-05 19:59 UTC
9	rebase	0349b1d → c3fc948		2026-05-06 10:57 UTC
10	content	c3fc948 → 6421363		2026-05-06 13:00 UTC
11	rebase	6421363 → ece765d		2026-05-07 13:40 UTC
12	rebase	ece765d → cc96b9a		2026-05-07 15:17 UTC
13	rebase	cc96b9a → 45c9d93		2026-05-07 18:21 UTC