refactor: add service layer architecture with Pydantic validation

- Add services layer (PartyService, ScheduleService, ProductService, ServiceCenterService)
- Add ServiceProvider for dependency injection
- Add Pydantic input validation on all MCP tools
- Add thread-safety to TrytonSettings with double-checked locking
- Update tests to mock ServiceProvider instead of direct client calls
- Add pydantic dependency

src/tryton_mcp/services/base.py

@@ -0,0 +1,28 @@
+from typing import Any, Dict, List, Optional
+from dataclasses import dataclass
+
+
+@dataclass
+class TrytonResponse:
+    success: bool
+    data: Any = None
+    error: Optional[str] = None
+
+    @property
+    def is_error(self) -> bool:
+        return not self.success
+
+
+class BaseService:
+    def __init__(self, client: Any):
+        self._client = client
+
+    def call(self, method: str, args: List[Any]) -> TrytonResponse:
+        try:
+            response = self._client.call(method, args)
+            return TrytonResponse(success=True, data=response)
+        except Exception as e:
+            return TrytonResponse(success=False, error=str(e))
+
+    def _get_client(self) -> Any:
+        return self._client