refactor!: remove gov keeper.MustMarshal

[robert-zaremba]

Description

Cleaning API. Must* methods should be avoided in a public interface, especially if they are used only in one place.

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Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.

I have...

• included the correct type prefix in the PR title
• added ! to the type prefix if API or client breaking change
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• followed the guidelines for building modules
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• included comments for documenting Go code
• updated the relevant documentation or specification
• reviewed "Files changed" and left comments if necessary
• confirmed all CI checks have passed

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.

I have...

• confirmed the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)

[codecov]

Codecov Report

Merging #10373 (4438dcd) into master (3c85944) will decrease coverage by 0.00%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master   #10373      +/-   ##
==========================================
- Coverage   64.28%   64.27%   -0.01%     
==========================================
  Files         572      572              
  Lines       54239    54230       -9     
==========================================
- Hits        34867    34859       -8     
+ Misses      17390    17389       -1     
  Partials     1982     1982              

Impacted Files	Coverage Δ
x/gov/keeper/proposal.go	79.71% <33.33%> (-1.25%)	⬇️
crypto/keys/internal/ecdsa/privkey.go	84.21% <0.00%> (+1.75%)	⬆️

[tac0turtle]

utACk. Thank you for this cleanup

[robert-zaremba]

It came after reading more about gov router.