Issue being fixed or feature implemented

It would be nice if clients (like dash-evo-tool) could know the actual fees paid for state transitions without having to fetch identity balances before and after. Something similar to how Ethereum returns gasUsed in transaction receipts. Previously, WaitForStateTransitionResultResponse only returned proof or error without the fee breakdown, even though the fee information was calculated internally in StateTransitionExecutionResult::SuccessfulExecution.

What was done?

• Proto: Added FeeResult message with processing_fee, storage_fee, and removed_from_system fields. Added optional fee_result field to WaitForStateTransitionResultResponseV0.

• Drive: Encode fee result into ExecTxResult.data during state transition execution (20 bytes: 8 + 8 + 4 for processing_fee, storage_fee, removed_bytes). Included for both successful executions and paid consensus errors.

• DAPI: Decode fee data from Tenderdash transaction results (both websocket events and existing tx queries). Populate fee_result field in gRPC responses for success and paid error cases.

• SDK: Added FeeResult struct and StateTransitionBroadcastResult wrapper. Added new trait methods broadcast_and_wait_with_fee() and wait_for_response_with_fee() that return fee information alongside the proof result. Existing methods unchanged for backwards compatibility.

How Has This Been Tested?

• Unit tests added for fee encoding in Drive (test_encode_fee_result, test_encode_fee_result_zero_values, test_encode_fee_result_max_values)
• Unit tests added for fee decoding in DAPI (test_decode_fee_result_valid, test_decode_fee_result_zero_values, test_decode_fee_result_too_short, test_decode_fee_result_empty, test_decode_fee_result_extra_bytes)
• Unit tests added for SDK FeeResult conversion (test_fee_result_from_grpc, test_fee_result_total_no_overflow)
• All tests pass with cargo test

Breaking Changes

None - existing broadcast_and_wait() and wait_for_response() methods remain unchanged. New methods are additive.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have added "!" to the title and described breaking changes in the corresponding section if my code contains any
• I have made corresponding changes to the documentation if needed

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone