TBD: Looser coupling between L2 blocks and L1 origin

[alfonso-op]

Amend chain derivation rules such that not every L1 block needs to serve as a unique origin for L2 blocks. Instead, the L1 origin should be able to represent a range of L1 blocks, allowing L2 block times to be better decoupled from the L1

This capability may best be built leveraging the proposed deposit queue (see spec).

Additional context in this discussion thread.

Note: this is not a must for Holocene, hence P2 priority. We could try to at least implement and include the deposit queue in Holocene so we can target the L2/L1 decoupling in the subsequent hard fork.