fix(time): use McpError for proper JSON-RPC error propagation

Two fixes in the time server:

1. call_tool handler (line 216): Was raising plain ValueError instead of
   McpError. The MCP protocol requires JSON-RPC errors via McpError with
   proper error codes. A ValueError propagates as a generic internal error
   to the client, losing the error context.

2. get_zoneinfo (line 56): Catch KeyError specifically for unknown
   timezones vs. generic exceptions for invalid timezone strings. Gives
   the client more precise error messages ('Unknown timezone' vs
   'Invalid timezone').

Author: isheng-eqi

src/time/src/mcp_server_time/server.py

@@ -53,8 +53,10 @@ def get_local_tz(local_tz_override: str | None = None) -> ZoneInfo:
 def get_zoneinfo(timezone_name: str) -> ZoneInfo:
     try:
         return ZoneInfo(timezone_name)
+    except KeyError:
+        raise McpError(ErrorData(code=INVALID_PARAMS, message=f"Unknown timezone: {timezone_name}"))
     except Exception as e:
-        raise McpError(ErrorData(code=INVALID_PARAMS, message=f"Invalid timezone: {str(e)}"))
+        raise McpError(ErrorData(code=INVALID_PARAMS, message=f"Invalid timezone '{timezone_name}': {e}"))
 
 
 class TimeServer:
@@ -213,7 +215,7 @@ async def call_tool(
             ]
 
         except Exception as e:
-            raise ValueError(f"Error processing mcp-server-time query: {str(e)}")
+            raise McpError(ErrorData(code=INVALID_PARAMS, message=f"Error processing time query: {str(e)}"))
 
     options = server.create_initialization_options()
     async with stdio_server() as (read_stream, write_stream):