Add PartitionData reward type

[CriesofCarrots]

Problem

See problem description on #34624
The PDA that PR adds will be useful for clients querying a running RPC node for rewards. However, other clients may only have access to historical ledger.

Summary of Changes

Add a new RewardType::PartitionData to record the num_partitions in an optional Reward field. This reward gets written to the first block of an epoch (essentially replacing the list of stake and vote rewards in epochs before partitioned-rewards feature activation)
To find a specific reward, clients can examine the rewards in the first block of the epoch to get the num_partitions and use the previous_blockhash in the block metadata to create an EpochRewardsHasher.

• Needs rebase on Populate partitioned-rewards PDA during calculation #34624

[codecov]

Codecov Report

Attention: Patch coverage is 62.31884% with 26 lines in your changes are missing coverage. Please review.

Project coverage is 81.8%. Comparing base (4385ed1) to head (72951ca).
Report is 311 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #34761   +/-   ##
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  Coverage    81.8%    81.8%           
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  Files         825      825           
  Lines      223078   223140   +62     
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+ Hits       182497   182554   +57     
- Misses      40581    40586    +5     

[willhickey]

This repository is no longer in use. Please re-open this pull request in the agave repo: https://github.com/anza-xyz/agave