Add query write back capability to Python plugin API

[pauldix]

One of the common use cases for plugins is to do different kinds of downsampling into other tables. We should make this as easy and performant as possible with a special API. This will build on the work of #25757.

The Python side will look like:

def query_writeback(self, query: str, target_table: str, tags: List[str], parameters: : Optional[Dict[str, Any]] = None, query_database: Optional[str], target_database: Optional[str]) -> WriteBackResult

class WriteBackResult:
   def __init__(self, row_count: int, validation_errors: List[str], elapsed_time_ms: int):
       self.row_count = row_count
       self.validation_errors = validation_errors 
       self.elapsed_time_ms = elapsed_time_ms

The query and target databases default to whatever database the plugin trigger is tied to.

The Rust side should ensure that the query doesn't pull from the same table as the target, if the query and target databases are the same. It should execute the query and construct a WriteBatch from the results, updating the Catalog and writing the batch into the normal WAL write path.