Unwrap leading parenthesis in Statement.get_type() (fixes #727)

[ChrisJr404]

Fixes #727.

Statement.get_type() only looked at the first significant token. When a
statement is wrapped in parentheses, that token is the whole Parenthesis
group rather than a DML/DDL keyword, so the type came back as UNKNOWN:

>>> import sqlparse
>>> sqlparse.parse('(select 1 as "a") UNION (select 2 as "a")')[0].get_type()
'UNKNOWN'
>>> sqlparse.parse('select 1 as "a" UNION select 2 as "a"')[0].get_type()
'SELECT'

Parenthesized sub-selects like this (e.g. the sides of a compound UNION)
are common, so it is surprising that only the un-parenthesized form is
recognized.

Change

get_type() now unwraps a leading parenthesis before matching the keyword.
The loop handles nested parentheses (((select 1))) and skips the opening
punctuation together with any whitespace/comments inside. The existing CTE
handling now runs against the unwrapped container, so a WITH wrapped in
parentheses resolves too. Empty parentheses still report UNKNOWN.

>>> sqlparse.parse('(select 1) UNION (select 2)')[0].get_type()
'SELECT'
>>> sqlparse.parse('(INSERT INTO foo VALUES (1))')[0].get_type()
'INSERT'
>>> sqlparse.parse('()')[0].get_type()
'UNKNOWN'

Tests

Added test_gettype_parenthesized_statement_issue727 covering the reported
case plus nesting, a non-SELECT keyword, a leading comment, a parenthesized
CTE, and the empty-parentheses guard. The full suite passes (pytest), and
ruff check is clean on the changed module.