[stacks-signer] Remove unnecessary endpoint calls throughout the stacks signer

[jferrant]

Currently the stacks signer spams the endpoint at various points in the code base. A lot of this information should not change often and should not be queried on every pass of run one pass. For example, if the aggregate key is set for the reward cycle and approved in the contract, a signer should never have to query the node again for it.

Additionally, the stacker signer slots will be known during configuration and should not be retrieved on the fly when verifying transactions.