feat(stack): port stack push approvals decision to Rust

[jd]

mergify stack push skips its trunk-rebase whenever any PR in
the stack is already approved — a rebase force-pushes every
branch in the stack and would dismiss the reviews. The exception:
when the bottom PR has a real merge conflict with trunk, the
rebase has to happen anyway so the conflict gets surfaced. Both
--skip-rebase and --force-rebase are absolute overrides.

Port mergify_cli/stack/approvals.py to
mergify-stack::approvals:

• pull_is_approved — GET /repos/{u}/{r}/pulls/{n}/reviews
  with the same "latest review per reviewer wins" semantics as
  Python. A reviewer who once APPROVED and later requested
  changes counts as requested-changes; without that, a stale
  approve would falsely keep the PR in the approved set and a
  legitimate change request would get dismissed.
• fetch_approved_pull_numbers — sequential fan-out across the
  stack's live PRs (same secondary-rate-limit trade-off as
  remote_changes).
• bottom_pull_has_conflict — single GET with a 1s
  retry-once-on-null-mergeable to match GitHub's lazy mergeable
  computation. Any HTTP error coerces to false so a transient
  API hiccup can't force a surprise rebase.
• decide_rebase — the orchestrator: precedence is
  skip_rebase → force_rebase → approvals/conflict check.
  Returns a RebaseDecision with a typed RebaseReason enum
  for the CLI's "skipped because …" log line.

Coverage: 12 wiremock tests covering every branch of
decide_rebase plus the latest-review-wins semantics and the
HTTP-error coercion. Adds tokio (time feature only) and
url to mergify-stack's prod deps for the
mergeable-retry sleep and the wiremock test base-URL parse.

Co-Authored-By: Claude Opus 4.7 noreply@anthropic.com

Depends-On: #1535

[jd]

This pull request is part of a Mergify stack:

#	Pull Request	Link
1	feat(stack): port detect_change_type + patch-id helpers to Rust	#1532
2	feat(stack): port StackComment renderer to Rust	#1533
3	feat(stack): port replay git helpers (merge-tree + diff-tree) to Rust	#1534
4	feat(stack): port RevisionHistoryComment to Rust	#1535
5	feat(stack): port stack push approvals decision to Rust	#1536	👈
6	feat(stack): port replay HTTP upload + orchestrator to Rust	#1537
7	feat(stack): port stack push git plumbing (notes fetch + push) to Rust	#1539
8	feat(stack): port stack push rebase log lines to Rust	#1540
9	feat(stack): port format_pull_description + build_change_tasks to Rust	#1541
10	feat(stack): port create_or_update_pr + orphan branch delete to Rust	#1542
11	feat(stack): port per-PR stack + revision-history comment upserters to Rust	#1543
12	feat(stack): port stack push planner (get_changes) to Rust	#1544
13	feat(stack): port stack push orchestrator to Rust	#1545
14	feat(rust): wire native stack push + delete Python push.py	#1546
15	chore: delete Python tree + simplify wheel/CI for pure-Rust binary	#1547

[mergify]

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🔴 ⛓️ Depends-On Requirements

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• depends-on=Mergifyio/mergify-cli#1532 [⛓️ feat(stack): port detect_change_type + patch-id helpers to Rust #1532 [stack]]
• depends-on=Mergifyio/mergify-cli#1533 [⛓️ feat(stack): port StackComment renderer to Rust #1533 [stack]]
• depends-on=Mergifyio/mergify-cli#1534 [⛓️ feat(stack): port replay git helpers (merge-tree + diff-tree) to Rust #1534 [stack]]
• depends-on=Mergifyio/mergify-cli#1535 [⛓️ feat(stack): port RevisionHistoryComment to Rust #1535 [stack]]

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• depends-on=Mergifyio/mergify-cli#1532 [⛓️ feat(stack): port detect_change_type + patch-id helpers to Rust #1532 [stack]]
• depends-on=Mergifyio/mergify-cli#1533 [⛓️ feat(stack): port StackComment renderer to Rust #1533 [stack]]
• depends-on=Mergifyio/mergify-cli#1534 [⛓️ feat(stack): port replay git helpers (merge-tree + diff-tree) to Rust #1534 [stack]]
• depends-on=Mergifyio/mergify-cli#1535 [⛓️ feat(stack): port RevisionHistoryComment to Rust #1535 [stack]]

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