feat: add Query Builder date helpers

[memleakd]

Description

This proposes adding a small set of Query Builder helpers for filtering by parts of a date/datetime column:

$builder->whereDate('created_at', '2026-01-31');
$builder->whereYear('created_at', 2026);
$builder->whereMonth('created_at', 1);
$builder->whereDay('created_at', 31);

The matching OR variants are included as well: orWhereDate(), orWhereYear(), orWhereMonth(), and orWhereDay().

The main goal is to make a common query easier to write without asking users to remember the right SQL function for each database driver. The builder compiles the expression for the active driver, while still binding values and protecting identifiers by default.

A few details are documented explicitly:

• supported comparison operators can be added to the field name, like whereDate('created_at >=', '2026-01-01')
• null values use IS NULL / IS NOT NULL
• arrays and subqueries are not accepted for these helpers
• for large indexed timestamp columns, a range condition may still be more efficient

Tests cover the shared builder behavior, driver-specific SQL output, invalid inputs, DateTimeInterface values, grouped/or conditions, aliases before from(), and a live database query.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide