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-status.yml

@@ -0,0 +1,32 @@
+name: PR Hygiene
+
+on:
+  schedule:
+    - cron: "15 */12 * * *"
+  workflow_dispatch:
+
+permissions: {}
+
+concurrency:
+  group: pr-check-status
+  cancel-in-progress: true
+
+jobs:
+  nudge-stale-prs:
+    runs-on: blacksmith-2vcpu-ubuntu-2404
+    permissions:
+      contents: read
+      pull-requests: write
+      issues: write
+    env:
+      STALE_HOURS: "48"
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+
+      - name: Nudge PRs that need rebase or CI refresh
+        uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8
+        with:
+          script: |
+            const script = require('./.github/workflows/scripts/pr_check_status_nudge.js');
+            await script({ github, context, core });