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.

docker/docker-compose-env.yml

@@ -0,0 +1,19 @@
+version: '3.9'
+services:
+  cloudflare-ddns:
+    image: timothyjmiller/cloudflare-ddns:latest
+    container_name: cloudflare-ddns
+    security_opt:
+      - no-new-privileges:true
+    network_mode: 'host'
+    environment:
+      - CLOUDFLARE_API_TOKEN=your-api-token-here
+      - DOMAINS=example.com,www.example.com
+      - PROXIED=false
+      - TTL=1
+      - UPDATE_CRON=@every 5m
+      # - IP6_PROVIDER=none
+      # - HEALTHCHECKS=https://hc-ping.com/your-uuid
+      # - UPTIMEKUMA=https://kuma.example.com/api/push/your-token
+      # - SHOUTRRR=discord://token@webhook-id
+    restart: unless-stopped