refactor(pkg): canonicalize base types and adjust length handling

* Update base types to keep explicit modifier forms
* Modify length handling for vector types in tests

pkg/readers/drawdb/reader_test.go

@@ -317,7 +317,7 @@ func TestConvertToColumn_PreservesExplicitTypeModifiers(t *testing.T) {
 			name:       "custom vector modifier",
 			fieldType:  "vector(1536)",
 			wantType:   "vector(1536)",
-			wantLength: 1536,
+			wantLength: 0,
 		},
 	}