feat: Constrain block timestamp on L1 contract

[LHerskind]

The timestamp of the L2 block should be constrained by the L1 contract such that

• L2 timestamp > time of last block publication
  • To ensure that blocks are not built in a manner that progress time rollup time much slower than actual time.
  • This can be done by storing the lastBlockAt = block.timestamp at every publication, and for the next block ensure that l2 timestamp > lastBlockAt.
• L2 timestamp <= block.timestamp, should not be possible to push block into the future

I expect that this will mess quite a bit with test as timing now need to be added to the l2 blocks. For tests that are jumping time or expecting certain block times it might need to fetch block times directly.