ICRC-154: Standardizing Privileged Pause, Unpause & Deactivate Controls

[bogwar]

This PR introduces ICRC-524, a standard API for pausing, unpausing, and deactivating ledgers. It defines three privileged methods, canonical tx mapping, and use of block kinds from ICRC-124. The standard enables integrators to reliably query whether a ledger is paused or deactivated, and ensures that transitions are recorded and attributable on-chain.