Murisi/simplify namada masp rewards

[murisi]

Describe your changes

Experimented with modifying the reward distribution algorithm so that native token rewards are distributed in the same way as non-native tokens. Doing this causes a slight variation in the shielded rewards distributed for the default set of parameters and hence necessitated slight changes in the expectations of the integration tests.

At a high level, these changes mean that now all native tokens with an epoch other than 0 receive their rewards as epoch 0 native tokens (just the same as it's done for non-native tokens). The exception to this rule is epoch 0 native tokens, which have a direct conversion to the current epoch (i.e. a conversion term like 100NAM@ep30 - 10NAM@ep0). Hence reward claiming for everything except NAM@ep0 involves claiming a NAM@ep0 reward and then converting that to NAM@epN.

The following list describes the benefits/drawbacks of this approach:

• Benefit: simpler/shorter reward distribution code (due to native token branch being fused with non-native branch)
• Benefit: ability to claim rewards even for small amounts of NAM
  • Note: this benefit is small because these small amounts are insiginificant after inflation adjustment
• Drawback: the rewards become significantly less accurate over time as a "denominator" approaches 0
  • This "denominator" is the negative term of the native token conversion from epoch 0 to the current epoch

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

#2695

Checklist before merging to draft

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

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 9.18635% with 346 lines in your changes are missing coverage. Please review.

Project coverage is 53.32%. Comparing base (c733be2) to head (5890ef8). Report is 77 commits behind head on main.

Files	Patch %	Lines
crates/sdk/src/masp.rs	0.00%	332 Missing :warning:
crates/shielded_token/src/conversion.rs	71.42%	14 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2699      +/-   ##
==========================================
- Coverage   53.38%   53.32%   -0.06%     
==========================================
  Files         302      302              
  Lines      103403   103431      +28     
==========================================
- Hits        55198    55159      -39     
- Misses      48205    48272      +67     

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[brentstone]

what's the status of this? Is it still desired or necessary?

[murisi]

what's the status of this? Is it still desired or necessary?

It may be necessary. I'll be looking at integrating it soon.