Implement VarInt when getting signature payload

[Neylix]

Is your feature request related to a problem?

The node implemented the Var int system to provide an almost infinite number of entry in a list. archethic-foundation/archethic-node#408
This modification update the payload for transaction signature.

Describe the solution you'd like

Libjs have to add the Var int into the payload when signing a transaction.

Additional context

No response