Fee handling

[Nashtare]

Transaction fees are currently unsupported (or assuming no fees in Topos transactions) for the state-transition AIR program.

The easiest approaches seem to be either

• burn the fee (but may make total supply control tricky)
• send the fees to a dedicated account. Could be the first one in the Merkle tree, with a dedicated unreachable address. This implies adding the correct update of this account.

Approach two seems to be the preferred one.

[HarryTmetic]

Since subnets are sovereign entities, it could be left to the subnet (resp. initial) to choose its fee system for regular (resp. cross-subnet) TOPOS transactions.
For instance, no fee is paid in TOPOS, but rather the fee is paid in the native token of the subnet.