pallet-bounties: extends update_due infinitly if BountiesUpdatePeriod…

[BigTava]

… is None

Description

Fixes polkadot-fellows/runtimes#509

Integration

Remove BountyUpdatePeriod

Review Notes

Modifies how bounty expiry is handled

🔍 Code Diff Summary

- #[pallet::constant]
- type BountyUpdatePeriod: Get<BlockNumberFor<Self, I>>;
+ #[pallet::constant]
+ type BountyUpdatePeriod: Get<Option<BlockNumberFor<Self, I>>>;

- *update_due = (Self::treasury_block_number() + T::BountyUpdatePeriod::get()).max(*update_due);
+ *update_due = Self::treasury_block_number().saturating_add(
+     T::BountyUpdatePeriod::get().unwrap_or(BlockNumberFor::<T, I>::MAX)
+ ); 

Checklist

• My PR includes a detailed description as outlined in the "Description" and its two subsections above.
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• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)

[paritytech-workflow-stopper]

All GitHub workflows were cancelled due to failure one of the required jobs.
Failed workflow url: https://github.com/paritytech/polkadot-sdk/actions/runs/13550346591
Failed job name: test-linux-stable-runtime-benchmarks