[pallet-revive] Aggregate gas_cost for nested calls in execution tracer

[mokita-j]

Description

ExecutionTracer was reporting gasCost=0 for parent traces containing sub-calls. The gasCost should reflect the opcode cost plus the cumulative gas consumed by all sub-calls.

This PR:

• Aggregates gas_cost and weight_cost in ExecutionTracer for nested calls
• Adds test coverage for nested call gas tracking in both EVM and PVM modes

Review Notes

To check that ExecuteTracer has gasCost=0 for any *CALL trace. Run delegatecall-playground.ts

git clone https://github.com/paritytech/contracts-boilerplate.git
git checkout mj/trace-gas-cost-geth
# with revive node running
./cli/delegatecall-playground.ts

*This can also be checked in the benchmark reports, e.g. table.

To check Geth behaviour run the same script with geth node.