test: add balances delay (more balance changes) flow (#84)

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<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Adds new balance-delay upgrade/attest test flows (incl. 2-pool trace entries), renames the existing flow, and wires up corresponding fork tests; minor ideas doc cleanup.
> 
> - **Flows/Tests**:
>   - Add `BalancesDelayUpgradeAttestFlow` to verify staking power and rewards across epochs around an upgrade and attestations.
>   - Add `BalancesDelay2PoolTraceEntriesFlow` to cover multi-epoch, multi-increment scenarios (STRK+BTC) pre/post-upgrade.
>   - Rename and refactor `BalancesDelayFlow` -> `BalancesDelay1PoolTraceEntryFlow` (setup/test updated accordingly).
> - **Fork Tests**:
>   - Add `balances_delay_2_pool_trace_entries_flow_test` and `balances_delay_upgrade_attest_flow_test`.
>   - Replace `balances_delay_flow_test` with `balances_delay_1_pool_trace_entry_flow_test`.
> - **Docs**:
>   - Trim obsolete migration notes from `src/flow_test/flow_ideas.md`.
> 
> <sup>Written by [Cursor Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit 91fd529. This will update automatically on new commits. Configure [here](https://cursor.com/dashboard?tab=bugbot).</sup>
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Author: arad-starkware

src/flow_test/flow_ideas.md

@@ -15,10 +15,6 @@
 - staker change balance, attest, change balance, attest, set_v3, change balance, update_rewards, change_balance, update_rewards, test rewards.
 - with member from previous versions.
 
-## k=1 -> k=2 Migration Staker
-- staker in V2, update balance staker+update balance pool, upgrade, attest in current epoch, attest in next epoch, attest in next next epoch
-- staker in V2, advance epoch, update balance staker+update balance pool, advance epoch, update balance staker+update balance pool, upgrade, update balance staker+update balance pool, attest in current epoch, attest in next epoch, attest in next next epoch
-
 ## pool member balance at curr epoch migration
 - Member from V0, no actions in V1 or V2, test curr balance
 - Member from V1, no actions in V2, test curr balance