[Nakamoto] Support `pox-4` changes

[zone117x]

Some PoX contract functions (and events) will likely be updated with new fields as described at: https://github.com/stacksgov/sips/blob/feat/sip-021-nakamoto/sips/sip-021/sip-021-nakamoto.md#changes-to-pox

The changes aren't fully defined yet. This issue is tracking them:
stacks-network/stacks-core#3948

There will likely be new arguments/fields added to the PoX contract functions that the API is currently parsing and storing. If so, the API can ingest and expose these for the pox/stacking related endpoints.

[zone117x]

There are also likely changes needed for the Rosetta layer, e.g. when creating stacking transactions via Rosetta. TBD..

[zone117x]

Pox-4 support implemented and tested in #1754 and #1762

The pox-4 contract doesn't yet include signer arguments for the stacking functions described in SIP-021, that functionality is planned for the Argon milestone, and is being tracked here: stacks-network/stacks-core#3970

[zone117x]

The signer-key argument is being added to pox-4.clar functions in stacks-network/stacks-core#4209 (not yet merged)