feat: Key the across signature cache by the borrow digest

[BranimirTomeljak]

Description

A requeued non-exclusive across fill computes a fresh deadline each attempt, but the MPC signature cache was keyed by chain and deposit id only. The retry received the first attempt's signature paired with the new deadline and reverted on chain with InvalidSignature.

• BorrowSessionID keys the across signing session and cache by chainID, depositID, deadline, caller, borrowAmount, liquidityPool and repaymentChainId, so a fresh deadline misses the cache and triggers a new signing round.
• The across message handler and the status handler both derive the key through BorrowSessionID. Other protocols keep the legacy chain and deposit id key.

Deploy together with the sprinter-api change (https://github.com/sprintertech/sprinter-api/pull/1201).

Related Issue Or Context

Closes: #

How Has This Been Tested? Testing details.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation

Checklist:

• I have commented my code, particularly in hard-to-understand areas.
• I have ensured that all acceptance criteria (or expected behavior) from issue are met
• I have updated the documentation locally and in docs.
• I have added tests to cover my changes.
• I have ensured that all the checks are passing and green, I've signed the CLA bot

[github-actions]

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