fix(database/gdb): strip quote chars from schema in Model.TableFields (#4730)

## Summary

When performing cross-database JOINs with soft-delete, the schema name
parsed from `` `schema`.`table` `` format retains database-specific
quote characters. These quoted schema names break `information_schema`
WHERE clause queries in `TableFields` lookups.

This PR strips quote characters from `usedSchema` in
`Model.TableFields()`, matching the existing unquoting pattern used for
`usedTable` via `guessPrimaryTableName`.

## Changes

- `database/gdb/gdb_model_utility.go`: Add quote-stripping for
`usedSchema` using `gstr.Trim` with database-specific quote chars from
`GetChars()`

## Test

Existing `Test_Issue2338` in MySQL
(`contrib/drivers/mysql/mysql_z_unit_issue_test.go:685`) covers this
case. The MariaDB version exists in PR #4724 branch
(`contrib/drivers/mariadb/mariadb_z_unit_issue_test.go:688`), not yet
merged. Once both PRs are merged, the MariaDB test will also validate
this fix.

closes #4725

Co-authored-by: John Guo <claymore1986@gmail.com>

database/gdb/gdb_model_utility.go

@@ -37,6 +37,12 @@ func (m *Model) TableFields(tableStr string, schema ...string) (fields map[strin
 		usedTable  = m.db.GetCore().guessPrimaryTableName(tableStr)
 		usedSchema = gutil.GetOrDefaultStr(m.schema, schema...)
 	)
+	// Strip quote characters from schema name, as it may come from cross-database
+	// table parsing (e.g., `schema`.`table`) and contain database-specific quote chars.
+	charL, charR := m.db.GetChars()
+	if usedSchema != "" && (charL != "" || charR != "") {
+		usedSchema = gstr.Trim(usedSchema, charL+charR)
+	}
 	// Sharding feature.
 	usedSchema, err = m.getActualSchema(ctx, usedSchema)
 	if err != nil {