fix: skip unnecessary String cast on already-string search columns

src/fastapi_toolsets/crud/search.py

@@ -159,8 +159,11 @@ def build_search_filters(
         else:
             column = field
 
-        # Build the filter (cast to String for non-text columns)
-        column_as_string = column.cast(String)
+        # Build the filter (cast to String only when needed, to preserve
+        # pg_trgm GIN index usability on already-String columns)
+        column_as_string = (
+            column if isinstance(column.type, String) else column.cast(String)
+        )
         if config.case_sensitive:
             filters.append(column_as_string.like(f"%{query}%"))
         else: