SQL Expressions: Rework backend errors and error instrumentation (#109633)

* Capture error_type label on metrics/traces
* Make error messages more helpful to user
* Use errutil, categorized errors, and tie them to error_type (category in code)
* Misc trace fixes
* Add metric to track SQL input conversion

pkg/expr/sql/db_test.go

@@ -206,7 +206,7 @@ func TestErrorsFromGoMySQLServerAreFlagged(t *testing.T) {
 
 	_, err := db.QueryFrames(context.Background(), &testTracer{}, "sqlExpressionRefId", query, nil)
 	require.Error(t, err)
-	require.Contains(t, err.Error(), "error in go-mysql-server")
+	require.Contains(t, err.Error(), "error from the sql expression engine")
 }
 
 func TestFrameToSQLAndBack_JSONRoundtrip(t *testing.T) {
@@ -308,7 +308,7 @@ func TestQueryFrames_Limits(t *testing.T) {
 				CROSS JOIN (SELECT 1 AS val UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5) b
 			`,
 			opts:        []QueryOption{WithTimeout(1 * time.Nanosecond)},
-			expectError: "did not complete within the timeout",
+			expectError: "timed out",
 		},
 	}