feat: add request body hash helper and creator price snapshot tests

[dubemoyibe-star]

Request Body Idempotency Helper and Creator Price Snapshot Tests

Closes #517
Closes #504

Summary

This PR introduces a reusable request body hashing helper for generating stable idempotency keys and adds integration coverage for creator price snapshots.

Changes

Idempotency Helper

• Added hashRequestBody(body) helper using SHA-256.
• Returns a fixed-length hexadecimal hash.
• Produces consistent hashes for identical inputs.
• Added unit tests for:
  • identical objects
  • different objects
  • empty objects

Creator Price Snapshot Tests

• Added integration tests for creator detail responses.
• Verified current_price is sourced from snapshot data.
• Confirmed updated snapshots are reflected in API responses.
• Verified the field exists in both creator detail and creator list endpoints.

Validation

• Identical input produces the same hash.
• Different inputs generate different hashes.
• Empty objects return a valid hash.
• current_price matches the stored snapshot value.
• Updated snapshots are returned by subsequent requests.

Testing

• Added unit tests for request hashing.
• Added integration tests for creator price snapshots.
• All tests pass successfully.

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