client/rpc: small improvements

[tzemanovic]

Describe your changes

A quick follow-up for unresolved threads from #4205

Checklist before merging

• If this PR has some consensus breaking changes, I added the corresponding breaking:: labels
  • This will require 2 reviewers to approve the changes
• If this PR requires changes to the docs or specs, a corresponding PR is opened in the namada-docs repo
  • Relevant PR if applies:
• If this PR affects services such as namada-indexer or namada-masp-indexer, a corresponding PR is opened in that repo
  • Relevant PR if applies:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.46%. Comparing base (be0e986) to head (e67f96d).
Report is 66 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4223      +/-   ##
==========================================
+ Coverage   74.44%   74.46%   +0.01%     
==========================================
  Files         342      342              
  Lines      107785   107785              
==========================================
+ Hits        80243    80257      +14     
+ Misses      27542    27528      -14     

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