Add rewards query to SDK

[brentstone]

Describe your changes

Adds a query for a delegator or validator's rewards to the SDK

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 74.64%. Comparing base (b579d49) to head (a5a83f9).
Report is 23 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4213      +/-   ##
==========================================
+ Coverage   74.62%   74.64%   +0.01%     
==========================================
  Files         342      342              
  Lines      108554   108562       +8     
==========================================
+ Hits        81009    81034      +25     
+ Misses      27545    27528      -17     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.