fix(kms-connector): poll KMS response if request already exists

[eudelins-zama]

Closes https://github.com/zama-ai/fhevm-internal/issues/418

[Copilot]

Pull Request Overview

This PR fixes KMS connector error handling to properly handle cases where a KMS request already exists. Instead of treating AlreadyExists errors as recoverable and retrying, the code now recognizes this as a successful condition and proceeds to poll for the response.

• Updates error classification to treat AlreadyExists as recoverable for requests but not for responses
• Modifies retry logic to immediately return success when encountering AlreadyExists status
• Removes NotFound from recoverable response errors as it's no longer needed

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
processor.rs	Updates error classification logic for request and response status codes
kms_client.rs	Modifies retry loop to handle AlreadyExists as immediate success case

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[dartdart26]

Looks good!