opt: print error details in expropt test directive

Error details are now printed in the output of the `expropt` optimizer
test directive. This is helpful for seeing the formatted memo that is
included in the detail of the error that occurs when a memo cycle is
detected.

Release note: None

pkg/sql/opt/testutils/opttester/opt_tester.go

@@ -739,6 +739,9 @@ func (ot *OptTester) RunCommand(tb testing.TB, d *datadriven.TestData) string {
 	case "expropt":
 		e, err := ot.ExprOpt()
 		if err != nil {
+			if len(errors.GetAllDetails(err)) > 0 {
+				return fmt.Sprintf("error: %s\ndetails:\n%s", err, errors.FlattenDetails(err))
+			}
 			return fmt.Sprintf("error: %s\n", err)
 		}
 		ot.postProcess(tb, d, e)

pkg/sql/opt/xform/testdata/rules/cycle

@@ -16,3 +16,14 @@ expropt
 )
 ----
 error: memo group optimization passes surpassed limit of 100000; there may be a cycle in the memo
+details:
+memo (not optimized, ~3KB, required=[])
+ ├── G1: (memo-cycle-test-rel G2 G3) (memo-cycle-test-rel G1 G3)
+ ├── G2: (scan ab,cols=(1,2)) (scan ab@ab_b_idx,cols=(1,2))
+ │    └── []
+ │         ├── best: (scan ab,cols=(1,2))
+ │         └── cost: 1064.42
+ ├── G3: (filters G4)
+ ├── G4: (eq G5 G6)
+ ├── G5: (variable b)
+ └── G6: (const 1)