Investigate feasibility of storing EVM registers on transaction basis

[m-Peter]

Currently, the local state index, stores the EVM state changes per block, under a single register ID: https://github.com/onflow/flow-evm-gateway/blob/main/storage/pebble/register_storage.go#L80-L100 .

For certain cases, such as generating the trace of a transaction, it would be optimal if we can load the EVM for a given transaction index, on a given block. Now we are forced to replay all the preceding transactions in a given block, to generate the trace for the given transaction index: https://github.com/onflow/flow-evm-gateway/blob/main/api/debug.go#L331-L357 .

A good first step is to add some metrics, to count how many preceding transactions we need to replay, on average, before generating the requested transaction trace. And possibly measure the execution time as well.