[DoS] Reject BitName registrations without a matching reservation

[1440000bytes]

A BitName registration is only valid if it burns the reservation that commits to it. The spent reservation whose commitment equals keyed_hash(revealed_nonce, name_hash). Validation never enforced this: validate_bitnames / validate_reservations only check the counts of reservation and bitname inputs vs outputs.

As a result, a registration carrying a reservation input with a non-matching commitment (counts still balanced) passes validation, and then apply_registration panics while connecting the block. Because block connection runs inside the block-application write txn with no catch_unwind, this crashes the node.

Fix

• validate_bitnames now requires a spent reservation whose commitment matches the registration's implied commitment, returning a new NoReservationForRegistration error otherwise.
• apply_registration returns that error instead of .expect()-panicking, so no connection path can crash even if validation were bypassed.

Test

validate_bitnames_rejects_registration_without_matching_reservation builds a registration spending a reservation that commits to a different name and asserts it is rejected with NoReservationForRegistration, then confirms the same registration burning the correct reservation validates.

Verified the test fails against the unpatched code (the malicious registration is accepted by validation) and passes with the fix.