feat: add support for `DATE_TRUNC`

[janklan]

The subject says it all.

Summary by CodeRabbit

• New Features

  • Added DATE_TRUNC to truncate timestamps to specified precision with optional timezone support.

• Documentation

  • Updated integration guides (Doctrine, Laravel, Symfony) and usage examples showing DATE_TRUNC usage.

• Tests

  • Added unit and integration tests covering DATE_TRUNC SQL generation, argument validation, timezone handling, and multiple precision scenarios.

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