[pos] Add epoch argument to vp::pos::rewards (backport #4196)

[mergify]

Describe your changes

This adds an epoch argument to the rewards() function in vp::pos. It does require a RPC node update in order to work, but it's backwards compatible. Tested with previous build of namadan and results are same as before:

With node on main and client on this branch:

$ ./target/debug/namadac rewards --source tnam1qrtypl0yazfamk8ptmgp608msl8wzrkpmqwppc7w --validator tnam1qxsx2ezu89gx252kwwluqp7hadyp285tkczhaqg0
Current rewards available for claim: 4625.955882 NAM

With both client and node on this branch:

$ ./target/debug/namadac rewards --source tnam1qrtypl0yazfamk8ptmgp608msl8wzrkpmqwppc7w --validator tnam1qxsx2ezu89gx252kwwluqp7hadyp285tkczhaqg0
Current rewards available for claim: 4625.955882 NAM

$ ./target/debug/namadac rewards --source tnam1qrtypl0yazfamk8ptmgp608msl8wzrkpmqwppc7w --validator tnam1qxsx2ezu89gx252kwwluqp7hadyp285tkczhaqg0 --epoch 60
Rewards for epoch 60: 4625.955882 NAM

$ ./target/debug/namadac rewards --source tnam1qrtypl0yazfamk8ptmgp608msl8wzrkpmqwppc7w --validator tnam1qxsx2ezu89gx252kwwluqp7hadyp285tkczhaqg0 --epoch 59
Rewards for epoch 59: 3887.536527 NAM

$ ./target/debug/namadac rewards --source tnam1qrtypl0yazfamk8ptmgp608msl8wzrkpmqwppc7w --validator tnam1qxsx2ezu89gx252kwwluqp7hadyp285tkczhaqg0 --epoch 58
Rewards for epoch 58: 3148.755426 NAM

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: (coming soon)
• 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: feat: backfill epoch rewards namada-indexer#235

---

This is an automatic backport of pull request #4196 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 7937b91 has failed:

On branch mergify/bp/maint-libs-0.47/pr-4196
Your branch is ahead of 'origin/maint-libs-0.47' by 6 commits.
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You are currently cherry-picking commit 7937b91f6.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
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Unmerged paths:
  (use "git add <file>..." to mark resolution)
	added by them:   .changelog/libs-v0.47.0/SDK/4196-rewards-at-past-epoch.md

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.17%. Comparing base (3eca617) to head (62fe537).
Report is 17 commits behind head on maint-libs-0.47.

Additional details and impacted files

@@                 Coverage Diff                 @@
##           maint-libs-0.47    #4302      +/-   ##
===================================================
+ Coverage            74.07%   74.17%   +0.10%     
===================================================
  Files                  345      345              
  Lines               110155   110565     +410     
===================================================
+ Hits                 81592    82009     +417     
+ Misses               28563    28556       -7     

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