find a way to seal governance codec

[rigelrozanski]

ref #4451 (comment)
CC @alexanderbez, @fedekunze

it would be good to determine a way by which the governance codec could be sealed, currently it needs to remain unsealed such that other modules can register their custom proposal type with the gov codec... maybe each proposal type could also pass in a custom codec? ideas? this is a low priority issue I think

[alexanderbez]

Hmm, yeah this is a good point and particular only to governance atm. Imho, the plan is to ditch amino in the near future so this may not even be a concern by then. Until then, it's tricky because we cannot guarantee order of registrations because that depends on the order of when/which files are imported or loaded for the fist time. Regardless, I do think this is low priority.