Add traces for flashblocks block building execution #124
Description
Now that we merge support for otel tracing #31 we should try to generate traces for the Flashblocks execution. This is an example of traces generated early on with a Go Flashblocks builder.
A new span is crated for each flashblock and the traces are combined with the traces from Rollup-boost. For now, this issue focuses on the flashblocks traces.
