feat(proof): enhance aggregation request handling with prover isolation

[smtmfft]

• Updated AggregationRequestKey to include an optional prover address for isolating aggregate proofs per prover.
• Modified batch_handler and shasta_batch_handler to utilize the new new_with_image_id_and_prover method for creating aggregation keys, allowing for more granular proof management based on the prover.

[Copilot]

Pull request overview

This PR aims to prevent aggregation-task key collisions across different provers by extending AggregationRequestKey with an optional prover_address, and wiring that into the v3 batch/Shasta batch aggregation flows.

Changes:

• Extend AggregationRequestKey with optional prover_address and add a constructor that sets both image_id and prover.
• Update v3 /batch handler to build aggregation keys with the prover address.
• Update v3 Shasta batch handler to (a) reuse cached guest inputs and (b) build aggregation keys with the prover address.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
reqpool/src/request.rs	Adds prover_address: Option<String> to AggregationRequestKey and a new constructor to include it.
host/src/server/api/v3/proof/shasta_handler.rs	Refactors Shasta batch flow to always run the input step first and uses prover-isolated aggregation keys.
host/src/server/api/v3/proof/batch_handler.rs	Uses the new prover-isolated aggregation key constructor for batch aggregation.

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