checked assign ops

[tzemanovic]

Describe your changes

A small refactor of assign ops to use the newly supported checked assign ops in smooth-operator.

Indicate on which release or other PRs this topic is based on

v0.39.0

Checklist before merging to draft

• I have added a changelog
• Git history is in acceptable state

[codecov]

Codecov Report

Attention: Patch coverage is 53.57143% with 13 lines in your changes missing coverage. Please review.

Project coverage is 53.92%. Comparing base (879a326) to head (183aa61).

Files	Patch %	Lines
crates/sdk/src/queries/vp/pos.rs	0.00%	11 Missing ⚠️
crates/governance/src/utils.rs	83.33%	1 Missing ⚠️
crates/sdk/src/rpc.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3374      +/-   ##
==========================================
- Coverage   53.92%   53.92%   -0.01%     
==========================================
  Files         317      317              
  Lines      107575   107567       -8     
==========================================
- Hits        58011    58003       -8     
  Misses      49564    49564              

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The merge-base changed after approval.