SQL objects from get_sql() have no parsed expression, breaking select_with_total()

[cofin]

Description

SQL objects loaded from .sql files via db_manager.get_sql('query-name') have expression=None, but select_with_total() requires a parsed expression to create COUNT queries.

Steps to Reproduce

1. Load SQL files with db_manager.load_sql_files('/path/to/sql')
2. Get a SQL object with sql = db_manager.get_sql('my-query')
3. Call driver.select_with_total(sql, *filters, schema_type=MySchema)

Expected Behavior

The SQL object should either:

• Have its expression attribute populated by parsing the SQL string
• Or _create_count_query() should handle raw SQL strings without a parsed expression

Actual Behavior

sql = db_manager.get_sql('list-users')
print(sql.sql)  # Returns valid SQL string: 'SELECT id, email... FROM user_account'
print(sql.expression)  # Returns: None

When select_with_total() is called, it fails with:

sqlspec.exceptions.ImproperConfigurationError: Cannot create COUNT query from empty SQL expression

The error comes from _create_count_query() in driver/_common.py:

def _create_count_query(self, original_sql: "SQL") -> "SQL":
    if not original_sql.expression:
        msg = "Cannot create COUNT query from empty SQL expression"
        raise ImproperConfigurationError(msg)

Environment

• SQLSpec version: 0.32.0 (from main branch)
• Python: 3.12

Workaround

None known - SQL file-based queries cannot use select_with_total()/pagination with count.

[cofin]

Fixed in #284