fix(sqltypes): serialize SqlTimeStamp as RFC3339

Marshal JSON/YAML/XML and driver Value now emit time.RFC3339 instead of
the offset-less "2006-01-02T15:04:05" layout; zero-time guards compare
against the RFC3339 zero value. Parsing is unchanged and still accepts
bare datetimes.

pkg/sqltypes/sql_types.go

@@ -445,21 +445,21 @@ type (
 	SqlUUID      = SqlNull[uuid.UUID]
 )
 
-// SqlTimeStamp - Timestamp with custom formatting (YYYY-MM-DDTHH:MM:SS).
+// SqlTimeStamp - Timestamp serialized as RFC3339.
 type SqlTimeStamp struct{ SqlNull[time.Time] }
 
 func (t SqlTimeStamp) MarshalJSON() ([]byte, error) {
 	if !t.Valid || t.Val.IsZero() || t.Val.Before(time.Date(0o002, 1, 1, 0, 0, 0, 0, time.UTC)) {
 		return []byte("null"), nil
 	}
-	return fmt.Appendf(nil, `"%s"`, t.Val.Format("2006-01-02T15:04:05")), nil
+	return fmt.Appendf(nil, `"%s"`, t.Val.Format(time.RFC3339)), nil
 }
 
 func (t *SqlTimeStamp) UnmarshalJSON(b []byte) error {
 	if err := t.SqlNull.UnmarshalJSON(b); err != nil {
 		return err
 	}
-	if t.Valid && (t.Val.IsZero() || t.Val.Format("2006-01-02T15:04:05") == "0001-01-01T00:00:00") {
+	if t.Valid && (t.Val.IsZero() || t.Val.Format(time.RFC3339) == "0001-01-01T00:00:00Z") {
 		t.Valid = false
 	}
 	return nil
@@ -469,21 +469,21 @@ func (t SqlTimeStamp) Value() (driver.Value, error) {
 	if !t.Valid || t.Val.IsZero() || t.Val.Before(time.Date(0o002, 1, 1, 0, 0, 0, 0, time.UTC)) {
 		return nil, nil
 	}
-	return t.Val.Format("2006-01-02T15:04:05"), nil
+	return t.Val.Format(time.RFC3339), nil
 }
 
 func (t SqlTimeStamp) MarshalYAML() (any, error) {
 	if !t.Valid || t.Val.IsZero() || t.Val.Before(time.Date(0o002, 1, 1, 0, 0, 0, 0, time.UTC)) {
 		return nil, nil
 	}
-	return t.Val.Format("2006-01-02T15:04:05"), nil
+	return t.Val.Format(time.RFC3339), nil
 }
 
 func (t *SqlTimeStamp) UnmarshalYAML(value *yaml.Node) error {
 	if err := t.SqlNull.UnmarshalYAML(value); err != nil {
 		return err
 	}
-	if t.Valid && (t.Val.IsZero() || t.Val.Format("2006-01-02T15:04:05") == "0001-01-01T00:00:00") {
+	if t.Valid && (t.Val.IsZero() || t.Val.Format(time.RFC3339) == "0001-01-01T00:00:00Z") {
 		t.Valid = false
 	}
 	return nil
@@ -493,7 +493,7 @@ func (t SqlTimeStamp) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
 	if !t.Valid || t.Val.IsZero() || t.Val.Before(time.Date(0o002, 1, 1, 0, 0, 0, 0, time.UTC)) {
 		return e.EncodeElement("", start)
 	}
-	return e.EncodeElement(t.Val.Format("2006-01-02T15:04:05"), start)
+	return e.EncodeElement(t.Val.Format(time.RFC3339), start)
 }
 
 func (t *SqlTimeStamp) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
@@ -511,7 +511,7 @@ func (t *SqlTimeStamp) UnmarshalXML(d *xml.Decoder, start xml.StartElement) erro
 		return err
 	}
 	t.Val = tm
-	t.Valid = !tm.IsZero() && tm.Format("2006-01-02T15:04:05") != "0001-01-01T00:00:00"
+	t.Valid = !tm.IsZero() && tm.Format(time.RFC3339) != "0001-01-01T00:00:00Z"
 	return nil
 }
 

pkg/sqltypes/sql_types_test.go

@@ -178,7 +178,7 @@ func TestSqlTimeStamp_JSON(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Marshal failed: %v", err)
 	}
-	expected := `"2024-01-15T10:30:45"`
+	expected := `"2024-01-15T10:30:45Z"`
 	if string(data) != expected {
 		t.Errorf("expected %s, got %s", expected, string(data))
 	}

pkg/sqltypes/sql_types_yaml_xml_test.go

@@ -195,7 +195,7 @@ func TestSqlTimeStamp_YAML(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Marshal failed: %v", err)
 	}
-	if string(data) != "2024-06-15T09:30:00\n" {
+	if string(data) != "\"2024-06-15T09:30:00Z\"\n" {
 		t.Errorf("unexpected YAML: %q", string(data))
 	}
 	var ts2 SqlTimeStamp