Add NOT NULL constraints to column_types primary key columns

SQLite allows NULLs in primary key columns by default, so mark
database_name, resource_name, and column_name as NOT NULL explicitly.

https://claude.ai/code/session_01SvPEPqHgURTWESRp28pTC3

datasette/utils/internal_db.py

@@ -105,9 +105,9 @@ async def initialize_metadata_tables(db):
         );
 
         CREATE TABLE IF NOT EXISTS column_types (
-            database_name TEXT,
-            resource_name TEXT,
-            column_name TEXT,
+            database_name TEXT NOT NULL,
+            resource_name TEXT NOT NULL,
+            column_name TEXT NOT NULL,
             column_type TEXT NOT NULL,
             config TEXT,
             PRIMARY KEY (database_name, resource_name, column_name)