test: block rewards by timestamp flows

[noa-starkware]

Note

Low Risk
Changes are confined to test flows and test harness utilities; primary risk is brittle/incorrect assumptions in new reward calculations or role setup causing flaky tests rather than production impact.

Overview
Adds several new flow tests in flow_test/test.cairo to validate timestamp-based rewards behavior: average block duration calculation across mixed block times, identical rewards within the same epoch, correct accrual when update_rewards skips blocks/epochs, and reward changes when updating epoch length or the reward supplier’s block-duration config.

Updates the flow-test harness (flow_test/utils.cairo) to support new reward-supplier governance roles (app_role_admin, app_governor) and exposes a helper to call set_block_duration_config via the config dispatcher. Test utilities add split_pool_rewards and clarify avg_block_time units used by calculate_current_block_rewards_with_avg_block_time_v3.

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This change is 

[remollemo]

@remollemo reviewed 19 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 95.91%. Comparing base (24da68f) to head (ad43fab).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #98      +/-   ##
==========================================
+ Coverage   95.80%   95.91%   +0.10%     
==========================================
  Files          43       43              
  Lines       10517    10797     +280     
==========================================
+ Hits        10076    10356     +280     
  Misses        441      441              

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