Convert remaining procedural hooks to OOP hooks

Problem/Motivation

• one_time_password.module still contains four procedural hook implementations, each tagged #[LegacyHook] and forwarding to an equivalent method already implemented in src/Hook/OneTimePasswordHooks.php.
• #[LegacyHook] only exists to support Drupal core versions older than 11.1.0, where attribute-based hooks aren't available.
• The module's core_version_requirement is ^11.3 || ^12, so no supported version of core will ever execute these procedural fallbacks, making them dead code.
• Separately, one_time_password.install implements hook_requirements() procedurally, but only ever returns data for the runtime phase.

Steps to reproduce

Proposed resolution

• The one_time_password.module file will be deleted, since it will contain no remaining logic once the legacy stubs are removed.
• hook_requirements() will be replaced with an OOP #[Hook('runtime_requirements')] implementation on OneTimePasswordHooks, dropping the now-unnecessary $phase check.
• hook_install() will remain procedural in one_time_password.install, as Drupal core does not support class-based/attribute implementations of install-time hooks.
• The kernel test covering requirements will be updated to invoke the hook via \Drupal::moduleHandler()->invoke() instead of calling the removed procedural function directly.

Remaining tasks

User interface changes

API changes

Data model changes