Compute worker should also submit commitment to BFT roothash

[kostko]

The compute worker currently only submits its commitment to the merge committee. It should also submit it to BFT roothash by using ComputeCommit after a timeout has elapsed and no new blocks have been seen.

This serves the purpose of time-stamping the compute commitment in case the merge committee claims it didn't see it. (Note that this should only happen in case the compute worker is unable to reach any honest merge commitee nodes.)

This requires that we store the write logs in storage and/or use the 3-way merge of roots at the merge committee (e.g., the compute committee cannot just send write logs to the merge committee).