fix(grpc): Read method from handler_call_details for grpcio >= 1.76 compat

grpcio 1.76 introduced registered method handlers which resolve RPC
methods at the C-core level. For these methods,
`context._rpc_event.call_details.method` is empty, breaking tracing.

This fix aligns the sync ServerInterceptor with the async version by:
1. Storing handler_call_details in intercept_service
2. Reading method from handler_call_details instead of context._rpc_event

The async ServerInterceptor already uses this approach and works correctly.

Fixes #5520

Author: yeung108

sentry_sdk/integrations/grpc/server.py

@@ -22,7 +22,7 @@ def __init__(
         self: "ServerInterceptor",
         find_name: "Optional[Callable[[ServicerContext], str]]" = None,
     ) -> None:
-        self._find_method_name = find_name or ServerInterceptor._find_name
+        self._find_method_name = find_name or self._find_name
 
         super().__init__()
 
@@ -31,6 +31,7 @@ def intercept_service(
         continuation: "Callable[[HandlerCallDetails], RpcMethodHandler]",
         handler_call_details: "HandlerCallDetails",
     ) -> "RpcMethodHandler":
+        self._handler_call_details = handler_call_details
         handler = continuation(handler_call_details)
         if not handler or not handler.unary_unary:
             return handler
@@ -64,6 +65,9 @@ def behavior(request: "Message", context: "ServicerContext") -> "Message":
             response_serializer=handler.response_serializer,
         )
 
-    @staticmethod
-    def _find_name(context: "ServicerContext") -> str:
-        return context._rpc_event.call_details.method.decode()
+    def _find_name(self: "ServerInterceptor", context: "ServicerContext") -> str:
+        # type: ignore[override]
+        # Read method from handler_call_details instead of context._rpc_event
+        # because grpcio >= 1.76 returns empty method for registered handlers
+        # via context._rpc_event.call_details.method
+        return self._handler_call_details.method