Implement E2E tests for `paras` pallet operations

[rockbmb]

Summary

Implement end-to-end tests for parachain lifecycle and administrative operations managed by the paras pallet.

Background

The paras pallet handles critical parachain lifecycle operations including validation code management, head data updates, and administrative functions.
Not all of these can be tested, but having the testable ones in PET is positive to identify failing CUJs/CUIs involving parachains.

Functions to consider testing

• force_set_current_code: Root authority immediately updates parachain validation code without waiting for normal upgrade process
• force_set_current_head: Root authority directly updates parachain head data for emergency state recovery
• force_schedule_code_upgrade: Root schedules code upgrade to take effect at specific relay parent block number
• force_note_new_head: Root manually notes new head for parachain within current block context
• force_queue_action: Root forces parachain into next session's action queue for immediate processing
• add_trusted_validation_code: Root adds validation code to storage with reference count 0 for emergency deployments
• poke_unused_validation_code: Root removes unused validation code to prevent storage leaks

Test Scenarios

• Validation code upgrade
• Upgrade cooldown changes