refactor(sqs): extract create_queue validation and redrive-policy helpers

[vieiralucas]

Summary

`create_queue` had three inline validation blocks that each deserved to be its own function:

• DelaySeconds (0–900) and MaximumMessageSize (1024–1 MiB) validation → `validate_create_queue_attributes`.
• `RedrivePolicy` JSON parsing (the 12-line closure that pulled `deadLetterTargetArn` and a `maxReceiveCount` coerced from either a number or a string) → `parse_redrive_policy`.
• `RedrivePolicy` target validation (DLQ must exist, and a FIFO source cannot use a standard DLQ) → `validate_redrive_policy_target`.

`create_queue` itself gets 80 lines shorter. No behavior change — same `AwsServiceError` codes, same messages (including the `AWS.SimpleQueueService.NonExistentQueue` `x-amzn-query-error` header on the DLQ-not-found path), same order.

Test plan

• `cargo fmt`
• `cargo clippy --workspace --all-targets -- -D warnings`
• `cargo test -p fakecloud-sqs` (44 passed)

---

Summary by cubic

Refactored fakecloud-sqs to extract create_queue validation and redrive-policy logic into small helpers, making the function ~80 lines shorter with no behavior changes.

• Refactors
  • Moved DelaySeconds and MaximumMessageSize checks to validate_create_queue_attributes.
  • Added parse_redrive_policy to parse JSON and coerce maxReceiveCount from string or number.
  • Added validate_redrive_policy_target to verify DLQ exists and enforce FIFO-to-FIFO, preserving existing error codes/messages and the x-amzn-query-error header.

^{Written for commit 1fb1111. Summary will update on new commits.}

[cubic-dev-ai]

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