feat: remove optimistic recordIkaSig polling

[Rcc999]

Closes: #293
Merges into : #322

Summary by Sourcery

Handle IKA signature verification and rejection directly in the Sui event indexer and centralize Sui client creation for both indexing and redeem solving.

Bug Fixes:

• Clear stale sign IDs and allow retries when IKA signatures are rejected instead of leaving redeems blocked.

Enhancements:

• Verify completed IKA signatures on-chain from CompletedSignEvent and mark corresponding redeem inputs as verified.
• Look up redeem metadata by sign ID in storage to tie IKA events back to local redeem records.
• Share a common Sui client pool between the indexer and redeem solver, retrieving the minting signer mnemonic once at startup.
• Restrict solved redeem processing to inputs without a sign_id, delegating signature verification to the event handler.

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[robert-zaremba]

pre-approving. Let's update based on the comments, we will do a proper review in the #322