Enforce types when forming the scan tables (internal and output formatting)

Force all column types to ensure appropriate formatting for writing.  In
particular, no character data in place of integers, no floats, no
objects in place of strings.

Table formation for the functions
- st.joins_for_results
- st.joins_for_scans
- st.joins_for_projects
enforces types.

bin/sarif-extract-scans

@@ -104,7 +104,8 @@ external_info = ExternalInfo(
     scan_spec["project_id"],
     scan_spec["scan_id"],
     scan_spec["sarif_file_name"],
-    'deadbeef00',               # TODO: Take ql_query_id from where?
+    # TODO: Take ql_query_id from where? (git commit id of the ql query set)
+    'deadbeef00',               
 )
 
 #