fix(clickhouse): unwrap parenthesized PRIMARY_KEY independent of ORDER_BY

[anxkhn]

The ClickHouse engine adapter builds the PRIMARY KEY clause in
_build_table_properties_exp. When the PRIMARY_KEY physical property is a
single parenthesized column (for example PRIMARY_KEY = (a)), sqlglot parses it
into an exp.Paren that has to be unwrapped, otherwise the adapter emits a
doubly-parenthesized PRIMARY KEY ((a)).

The unwrap guard checked the wrong value: it tested ordered_by_raw (the
ORDER_BY value) for exp.Paren instead of primary_key. This looks like a
copy-paste leftover from the ORDER_BY block just above it, which correctly uses
ordered_by_raw. As a result the parenthesized PRIMARY_KEY was only unwrapped
when ORDER_BY happened to be a Paren too. With a bare column, a tuple, or no
ORDER_BY at all, the parentheses were kept and the generated primary key came
out malformed:

-- PRIMARY_KEY = (a) with ORDER_BY = a
-- before: ENGINE=MergeTree ORDER BY (a) PRIMARY KEY ((a))
-- after:  ENGINE=MergeTree ORDER BY (a) PRIMARY KEY (a)

So the emitted primary key wrongly depended on the unrelated ORDER_BY shape.

The fix checks primary_key for exp.Paren, making the PRIMARY_KEY block
symmetric with the ORDER_BY block above it. It is a one-line change to the
guard.

Test Plan

Added two regression assertions to
tests/core/engine_adapter/test_clickhouse.py::test_model_properties, pairing
PRIMARY_KEY = (a) with a bare ORDER_BY = a and with a tuple
ORDER_BY = (a, b); both now assert PRIMARY KEY (a). The existing case in that
test used ORDER_BY = (a) (also a Paren), which is exactly why the bug was
masked. Reverting the source line makes the new bare-ORDER_BY assertion fail
with PRIMARY KEY ((a)); restoring it passes.

pytest tests/core/engine_adapter/test_clickhouse.py::test_model_properties -q   # 1 passed
pytest tests/core/engine_adapter/test_clickhouse.py -q -m "not slow and not docker"   # 32 passed
make style   # passed

I did not mark the full make fast-test checklist item because the broad suite
is currently blocked in this local environment by an unrelated pyodbc / system
unixODBC import failure in
tests/core/test_connection_config.py::test_mssql_pyodbc_connection_string_generation.
The ClickHouse-specific regression coverage above passes.

Checklist

• I have run make style and fixed any issues
• I have added tests for my changes (if applicable)
• All existing tests pass (make fast-test)
• My commits are signed off (git commit -s) per the DCO