Investigate whether CrateStatement should inherit from Doctrine\DBAL\Statement

## Context

During the Doctrine DBAL 3 upgrade in PR #122, the statement wrapping now involves three layers:
1. `Doctrine\DBAL\Statement` (outer)
2. `Crate\DBAL\Driver\PDOCrate\CrateStatement` (middle)
3. `Crate\PDO\PDOStatement` (inner)

## Investigation Request

Investigate whether `CrateStatement` should inherit from `Doctrine\DBAL\Statement` instead of the current composition-based approach to potentially simplify the wrapping architecture.

## References

- PR: https://github.com/crate/crate-dbal/pull/122
- Comment: https://github.com/crate/crate-dbal/pull/122#discussion_r2538583696
- Requested by: @amotl

> The issue documents the current three-layer statement wrapping architecture and requests investigation into whether inheritance could simplify this design.

Start by reviewing PR #122 and its discussion, then trace the three statement layers named in the issue: Doctrine\DBAL\Statement, Crate\DBAL\Driver\PDOCrate\CrateStatement, and Crate\PDO\PDOStatement. Done means documenting whether inheritance is viable and recording the recommended wrapping architecture, with any relevant compatibility concerns.

Written by the indexing model from the issue text.