feat(rust): port ci git-refs and ci queue-info to native Rust (Phase 1.6)

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`.

PORT_STATUS.toml flips both entries to `native`. 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, port-inventory guard 4/4.

Change-Id: I8d3f96e6cb4eb51e6cd195951b3e622cee7efdd4

Author: jd

Cargo.lock

@@ -27,10 +27,6 @@
 # this file surfaces as a CI failure rather than a silent unshipped
 # port.
 
-[[command]]
-path = ["ci", "git-refs"]
-status = "shimmed"
-
 [[command]]
 path = ["ci", "junit-process"]
 status = "shimmed"
@@ -39,10 +35,6 @@ status = "shimmed"
 path = ["ci", "junit-upload"]
 status = "shimmed"
 
-[[command]]
-path = ["ci", "queue-info"]
-status = "shimmed"
-
 [[command]]
 path = ["ci", "scopes"]
 status = "shimmed"

PORT_STATUS.toml

@@ -13,7 +13,9 @@ publish = false
 mergify-core = { path = "../mergify-core" }
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
+serde_yaml_ng = "0.10"
 url = "2"
+uuid = { version = "1", features = ["v4"] }
 
 [dev-dependencies]
 tempfile = "3.14"