chore(ci): externalize workflow scripts and relocate main flow doc (#722)

* feat: Add GitHub Actions workflows for security audits, CodeQL analysis, contributor updates, performance benchmarks, integration tests, fuzz testing, and reusable Rust build jobs

- Implemented `sec-audit.yml` for Rust package security audits using `rustsec/audit-check` and `cargo-deny-action`.
- Created `sec-codeql.yml` for CodeQL analysis scheduled twice daily.
- Added `sync-contributors.yml` to update the NOTICE file with new contributors automatically.
- Introduced `test-benchmarks.yml` for performance benchmarks using Criterion.
- Established `test-e2e.yml` for running integration and end-to-end tests.
- Developed `test-fuzz.yml` for fuzz testing with configurable runtime.
- Created `test-rust-build.yml` as a reusable job for executing Rust commands with customizable parameters.
- Documented main branch delivery flows in `main-branch-flow.md` for clarity on CI/CD processes.

* ci(workflows): update workflow scripts and rename for clarity; remove obsolete lint feedback script

* chore(ci): externalize workflow scripts and relocate main flow doc

.github/workflows/pr-check-stale.yml

@@ -0,0 +1,44 @@
+name: Stale PR Check
+
+on:
+    schedule:
+        - cron: "20 2 * * *"
+    workflow_dispatch:
+
+permissions: {}
+
+jobs:
+    stale:
+        permissions:
+            issues: write
+            pull-requests: write
+        runs-on: blacksmith-2vcpu-ubuntu-2404
+        steps:
+            - name: Mark stale issues and pull requests
+              uses: actions/stale@b5d41d4e1d5dceea10e7104786b73624c18a190f # v10.2.0
+              with:
+                  repo-token: ${{ secrets.GITHUB_TOKEN }}
+                  days-before-issue-stale: 21
+                  days-before-issue-close: 7
+                  days-before-pr-stale: 14
+                  days-before-pr-close: 7
+                  stale-issue-label: stale
+                  stale-pr-label: stale
+                  exempt-issue-labels: security,pinned,no-stale,no-pr-hygiene,maintainer
+                  exempt-pr-labels: no-stale,no-pr-hygiene,maintainer
+                  remove-stale-when-updated: true
+                  exempt-all-assignees: true
+                  operations-per-run: 300
+                  stale-issue-message: |
+                      This issue was automatically marked as stale due to inactivity.
+                      Please provide an update, reproduction details, or current status to keep it open.
+                  close-issue-message: |
+                      Closing this issue due to inactivity.
+                      If the problem still exists on the latest `main`, please open a new issue with fresh repro steps.
+                  close-issue-reason: not_planned
+                  stale-pr-message: |
+                      This PR was automatically marked as stale due to inactivity.
+                      Please rebase/update and post the latest validation results.
+                  close-pr-message: |
+                      Closing this PR due to inactivity.
+                      Maintainers can reopen once the branch is updated and validation is provided.