Fix grouping of datetime cast timezone suffixes

[SAY-5]

Fixes #811.

SELECT '2020-01-01'::timestamp WITH TIME ZONE AS moment, ARRAY(SELECT 1) AS items; currently leaves the timezone suffix outside the cast. The SELECT list then starts at the alias, and reindent places ARRAY 49 spaces from the left edge instead of 7.

Extend :: casts of TIME/TIMESTAMP, including optional precision, through a complete WITH/WITHOUT TIME ZONE suffix. Preserve the original tokens and keep unaliased casts from reporting the operand or type name as an alias. The regression tests cover formatting, comments, explicit and implicit aliases, chained casts, custom types, CTEs, and subsequent AT TIME ZONE conversion.

This change is limited to PostgreSQL-style :: casts. It does not change CAST expressions, typed literals, or AT TIME ZONE tokenization.

Validation on macOS with Python 3.13.0: 570 passed, 2 xfailed, 1 xpassed; Ruff passed. The 64 focused cases produce 45 failures and 19 passes on untouched master, then all pass with the fix. The grouping benchmark and bounded datetime-cast parsing/formatting benchmarks report linear scaling. Other Python versions and platforms were not run locally.

This change was developed with AI assistance.

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