Rollup node: compact snapshots with context reconstruction

What

This MR introduces an option --compact to the snapshot export command to produce smaller snapshots for the rollup node.

Fixes #6818 (closed).

Why

The snapshots produced this way are smaller in size (by a factor at least 3) because they contain a single commit for the context corresponding to the first available level. Replaying the history of the context on import also guarantees that the PVM state is correct (if the L2 blocks of the snapshots are also).

How

On import, the context is reconstructed by replaying all L2 blocks since the first available level. This takes longer than importing a snapshot produced without --compact (a few minutes instead of seconds). The correctness of the imported data is still checked afterwards but this phase is much quicker (a few seconds).

Example on ghostnet etherlink for "full" snapshot

Compact	size	export	import
No	1.4 GB	50s	20s
Yes	416 MB	39s	6m53s

Manually testing the MR

dune exec tezt/tests/main.exe -- -f sc_rollup.ml snapshot compact -i