Migrate cloudflare-ddns to Rust

Add Cargo.toml, Cargo.lock and a full src/ tree with modules and tests
Update Dockerfile to build a Rust release binary and simplify CI/publish
Remove legacy Python script, requirements.txt, and startup helper
Switch .gitignore to Rust artifacts; update Dependabot and workflows to
cargo
Add .env example, docker-compose env, and update README and VSCode
settings

Remove the old Python implementation and requirements; add a Rust
implementation with Cargo.toml/Cargo.lock and full src/ modules, tests,
and notifier/heartbeat support. Update Dockerfile, build/publish
scripts, dependabot and workflows, README, and provide env-based
docker-compose and .env examples.

.vscode/settings.json

@@ -11,11 +11,7 @@
     ".vscode": true,
     "Dockerfile": true,
     "LICENSE": true,
-    "requirements.txt": true,
-    "venv": true
+    "target": true
   },
-  "explorerExclude.backup": {},
-  "python.linting.pylintEnabled": true,
-  "python.linting.enabled": true,
-  "python.formatting.provider": "autopep8"
+  "explorerExclude.backup": {}
 }