Implement kaya-rbcs: simplified RBCS clone on the Kaya framework

- KayaApp with GET/PUT recursive routes backed by memcached (aiomcache)
- env-based configuration, metadata-aware value encoding, key prefix/digest
- Granian RSGI launcher (rbcs-server / python -m kaya_rbcs)
- pinned requirements via pip-compile, alpine:3.24 Dockerfile with healthcheck
- offline tests using an in-process fake memcached
- Gitea Actions workflow to build and push the multi-arch Docker image

.dockerignore

@@ -0,0 +1,12 @@
+.git
+.gitignore
+.venv
+**/__pycache__
+*.pyc
+.mypy_cache
+build
+dist
+*.egg-info
+tests
+Dockerfile
+.dockerignore