EIP-7685 - Refactor requests root generation

[anvacaru]

This PR fixes a bug in implementing EIP-7685 (General Purpose Execution Layer Requests) to conform to the reference implementations (process_general_purpose_requests).

• Fixed hash computation to properly follow the EIP-7685 two-step hashing process:
  • Hash each non-empty request type individually
  • Combine these digests for the final hash
• Updated deposit request handling to accumulate all deposits in a single Bytes object. The request_type byte is prepended before the requestRoot hash is computed.
• Changed DEPOSIT_REQUEST_TYPE from an Int to a Bytes constant for proper type consistency
• Modified <depositRequest> cell to use Bytes instead of List for request storage.

These changes ensure our KEVM implementation passes conformance tests and correctly implements both EIPs.
We will update the failing list of conformance tests after #2749 is merged.

[anvacaru]

Closing as these changes were incorporated in #2762 .