DAL/Rollups: fix refutation games

This MR fixes refutation games of DAL + rollups in several ways.

• First, a variant [Invalid_page_id] is added to DAL proofs. This variant is returned either when we manage to find the target cell but detect that importing the page (if it is attested) would be invalid, or when we do not manage to get the target cell but know (using the max / legacy attestation lag) that the page ID is invalid anyway.
• We no longer return [(None, None)] (meaning "no proof, no input required") but instead [(Invalid_proof_id, None)], where [None] means "no page to import" (equivalent to [Bytes.empty]).
• When checking the page ID, we now use the import level instead of the inbox commitment level.

With these fixes, all 36 tests in !19799 (merged) pass.

Test:

make && dune build tezt/lib_tezos && dune build tezt/tests && _build/default/tezt/tests/main.exe --file tezt/tests/sc_rollup.ml --match "dal_page_flipped_at_inbox_level_" -j 10