zero-cost/no-op gas meter

An infinite gas meter was added in !2976 (merged) to avoid out-of-gas panics. However, gas consumption is still tracked in the meter and used in consensus.

If we instead use a gas meter with a zero-cost config (i.e. a no-op meter), we can also remove the possibility of consensus failure on kv-store access changes.

This would allow us to change implementations as long as the final state of the store is correct. But this would only be possible going forward. Would like to get this in before hard fork so the next fork will not be tied unnecessarily to an implementation as we are today.

added hardfork label

assigned to @akrokr

unassigned @akrokr

(@akrokr , why was this unassigned? It still sounds convenient to be able to do KVStore Get refactors (e.g. for performance/simplicity) without LastResultsHash changes,
though changed-value Sets would necessarily still break sync and the AppHash.)