add limit() / offset() to CTE, as CTE.union() produces a CTE and not a CompoundSelect

Describe the bug
SQLAlchemy produces unwanted parentheses () when using UNION ALL which causes syntax errors in SQLite.

Expected behavior
UNION ALL clause produced without extra/wrapping parentheses.

To Reproduce

q = select([0]).union_all(select([0]).limit(30))

Produces:

SELECT ? UNION ALL (SELECT 0 LIMIT ? OFFSET ?)

(which leads to the error below).

The following SQL should be produced instead:

SELECT ? UNION ALL SELECT ? LIMIT ? OFFSET ?

Error

sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) near "(": syntax error
[SQL: SELECT 0 UNION ALL (SELECT 0
 LIMIT ? OFFSET ?)]
[parameters: (30, 0)]

Versions.

• OS: macOS v10.15.6
• Python: 3.8
• SQLAlchemy: v1.3.19
• Database: SQLite v3.31.1
• DBAPI: sqlite3

Additional context

• SQLAlchemy does not generate parentheses if no LIMIT clause is provided.

Start with the Python reproduction using select(), union_all(), limit(), and SQLite, then trace the SQL generation that adds parentheses around the limited SELECT. Run the reproduction against SQLite and verify that UNION ALL compiles without the unwanted wrapping parentheses while preserving LIMIT and OFFSET behavior.