clean up orphaned table namespaces (#29680)

In components push, we create a bunch of system and user tables in `start_push` that might not end up being used if `finish_push` is never called because of a validation error or other interruption. We should clean them up to avoid having tons of unused tables lying around.

GitOrigin-RevId: e73a29b9b435d70ae44131383445c18341a92700

crates/database/src/bootstrap_model/table.rs

@@ -223,7 +223,7 @@ impl<'a, RT: Runtime> TableModel<'a, RT> {
         Ok(())
     }
 
-    async fn get_table_metadata(
+    pub async fn get_table_metadata(
         &mut self,
         tablet_id: TabletId,
     ) -> anyhow::Result<ParsedDocument<TableMetadata>> {

crates/value/src/table_mapping.rs

@@ -119,6 +119,12 @@ impl TableMapping {
             })
     }
 
+    pub fn iter_active_namespaces(
+        &self,
+    ) -> impl Iterator<Item = (&TableNamespace, &OrdMap<TableName, TabletId>)> {
+        self.table_name_to_canonical_tablet.iter()
+    }
+
     pub fn namespaces_for_name(&self, name: &TableName) -> Vec<TableNamespace> {
         self.iter()
             .filter(|(_, _, _, table_name)| *table_name == name)