feat: calculate block rewards by timestamp

[noa-starkware]

This change is 

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Note

High Risk
Changes core reward distribution by caching per-epoch block rewards and sourcing them from timestamp-based avg block duration via RewardSupplier; mistakes could misprice rewards across epochs or break reward updates if epoch transitions aren’t handled correctly.

Overview
Block reward calculation is changed to be timestamp-based and epoch-cached. Staking now stores last_calculated_epoch and block_rewards, and update_rewards calls calculate_block_rewards(..., curr_epoch) which refreshes rewards only once per epoch by invoking RewardSupplier.update_current_epoch_block_rewards().

Test utilities and flow/tests are updated to advance both block number and timestamp (advance_blocks) and to compute expected V3 rewards directly from the minting curve using an average block duration (instead of dividing epoch rewards by epoch length). The V3 replaceability upgrade flow now also upgrades the RewardSupplier implementation.

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[remollemo]

@remollemo reviewed 7 files and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on NirLevi-starkware).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.78%. Comparing base (1d3ac9a) to head (76687b8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #66   +/-   ##
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  Coverage   95.78%   95.78%           
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  Files          42       42           
  Lines       10295    10299    +4     
=======================================
+ Hits         9861     9865    +4     
  Misses        434      434           

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