FR: add an `OperationTracer` at the end of the tx

[François Bojarski]

traceEndTransaction is a hook after the end of the transaction. We need a hook between the end of the execution and the end of the transaction, to get an access to:

• the account state (warmed address, balance, etc)
• the leftover gas
• the accrued Refund

[François Bojarski]

we can get it via traceContextExit and depth ==0