chore(ci): add stale issue triage workflow

[EliteCoder18]

Description

Follow-up to bitcoindevkit/bdk_wallet#497.

Adds .github/workflows/stale.yml, based on the workflow introduced in the referenced PR, to automatically label and close inactive issues and abandoned pull requests in this repository.

The workflow uses actions/stale@v11

• Issues inactive for 180 days -> marked stale -> closed after 30 additional days
• Pull requests inactive for 180 days -> marked stale -> closed after 30 additional days
• Issue exemptions: release, security, audit, do-not-close, and good first issue
• Pull request exemptions: blocked, security, and do-not-close
• Issues and pull requests associated with milestones are exempt
• Runs weekly on Mondays at 09:00 UTC
• Pull request runs are automatically forced into dry-run mode for safe validation
• Stale labels are removed when new activity occurs

The timing and exemption policy are initially kept consistent with bitcoindevkit/bdk_wallet#497. They can be adjusted based on feedback.

Notes to the reviewers

The workflow runs with debug-only: true on pull request events. I also recommend running it manually with debug_only=true after merging and reviewing the results before the first scheduled Monday run.

Changelog notice

ci: add automated stale issue and pull request triage

Checklists

All Submissions:

• I followed the contribution guidelines

[evanlinjin]

ConceptACK

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.36%. Comparing base (5108b5c) to head (5edb323).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2259   +/-   ##
=======================================
  Coverage   78.36%   78.36%           
=======================================
  Files          30       30           
  Lines        5945     5945           
  Branches      281      281           
=======================================
  Hits         4659     4659           
  Misses       1210     1210           
  Partials       76       76           

Flag	Coverage Δ
rust	78.36% <ø> (ø)

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