Cover edge cases in Registrar Pallet E2E tests

[naijauser]

Closes #629

This PR covers the following additional edge cases:

register

• User with insufficient balance cannot register para
• Cannot register para with validation code < MIN_CODE_SIZE
• Cannot register para with validation code > MAX_CODE_SIZE
• Cannot register para with genesis head > MAX_HEAD_DATA_SIZE
• Cannot register already registered para

deregister

• Deregistering an already-deregistered (non-existent) para fails with NotRegistered

add_lock / remove_lock

• Manager cannot lock an already-locked para
• Manager cannot remove lock
• Attempting to remove lock on a non-existent paraId is a no-op
• Test the add_lock / remove_lock cycle from the perspective of the para manager

swap

• Root origin can initiate and confirm a swap between two Parachains
• Para origin can initiate and confirm a swap between two Parachains
• Swapping a non-existent para ID fails with NotRegistered

schedule_code_upgrade

• Para itself can schedule a code upgrade even when locked
• Scheduling a code upgrade for a non-existent para fails with NotRegistered

set_current_head

• Setting the current head for a non-existent para fails with NotRegistered

[naijauser]

Hi @rockbmb, this is ready for review.

[github-actions]

No issues found. The changes are well-structured and the new tests cover a comprehensive set of edge cases for the registrar pallet as described. The code is clear and follows existing patterns in the project.

[rockbmb]

@naijauser will take a look ASAP!

[rockbmb]

LGTM, thanks!