change: Append block producer to log on block finalization

[AmbientTea]

Description

Adjustments for the block producer log pallet in anticipation of block reward payouts.

• Adds peek_prefix and drop_prefix operations to the block production log pallet
• Saves the block producer in a temporary storage and appends it to the block production log only in the on_finalize hook. This is to make the the prefix operations independent of pallet order in the runtime.

Checklist

• Commit sequence broadly makes sense and commits have useful messages.
• New tests are added if needed and existing tests are updated.
• Relevant logging and metrics added
• CI passes. See note on CI.
• Any changes are noted in the changelog.md for affected crate
• Self-reviewed the diff

Note on CI

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