Raise the reserved cycles limit of the ckBTC ledger canister

Proposal to change the reserved cycles limit of the ckBTC ledger canister

Target canister: mxzaz-hqaaa-aaaar-qaada-cai

New reserved cycles limit: 1_000_000_000_000_000_000

Previous ckBTC ledger proposal: https://dashboard.internetcomputer.org/proposal/143757

Motivation

Raise the reserved_cycles_limit of the ckBTC ledger canister from its current value of 5_000_000_000_000 (5T cycles, the default) to 1_000_000_000_000_000_000. The current value can be obtained by calling the canister_status endpoint of the NNS root canister.

Under subnet storage pressure, any memory growth is charged against this limit, and once the limit is reached the canister can no longer grow. The new limit is above the largest reservation the protocol could ever demand on this subnet, so it should not need revisiting.

Raising the limit neither reserves nor spends any cycles, and reservations remain bounded by the canister's actual cycles balance.