feat: add sandbox and local impl

backend/src/sandbox/local/local_sandbox_provider.py

@@ -0,0 +1,21 @@
+from src.sandbox.local.local_sandbox import LocalSandbox
+from src.sandbox.sandbox import Sandbox
+from src.sandbox.sandbox_provider import SandboxProvider
+
+_singleton: LocalSandbox | None = None
+
+
+class LocalSandboxProvider(SandboxProvider):
+    def acquire(self) -> Sandbox:
+        global _singleton
+        if _singleton is None:
+            _singleton = LocalSandbox("local")
+        return _singleton.id
+
+    def get(self, sandbox_id: str) -> None:
+        if _singleton is None:
+            self.acquire()
+        return _singleton
+
+    def release(self, sandbox_id: str) -> None:
+        pass