Drop Drupal 9 support

Drupal 9 reached end-of-life in November 2023. commerce_bluesnap still declares core_version_requirement: ^9.2 || ^10.0 || ^11 in commerce_bluesnap.info.yml, but the module isn't tested against D9 in CI, and there's no ongoing way to verify D9 compatibility as work continues on 3.x (SDK replacement, HTTP client rewrite, etc.).

This issue proposes dropping D9 support ahead of the first 3.x alpha release, so the module's declared compatibility matches what's actually verified, and so future 3.x work is free to use D10+-only APIs without version guards.

Proposed change:

-core_version_requirement: ^9.2 || ^10.0 || ^11
+core_version_requirement: ^10.3 || ^11

(^10.3 as the floor to match Commerce 3.x's own minimum, rather than ^10.0.)