DAL+Etherlink: prepare tests for increased latency

What

This MR increases the timeouts of Etherlink sequencer tests from 5 blocks to 20.

Stacked on !14087 (merged).

Why

This is a preparation for DAL integration in Etherlink. We need to increase the timeouts in order to wait enough blocks for the blueprints to be sent through the DAL. The added latency is:

• possibly one block for the rollup node to inject on the DAL,
• 8 blocks of lag to let DAL attesters attest the DAL slot (this is a DAL protocol parameter called "attestation_lag"),
• 1 block

Moreover, in !13883 (merged), the sequencer sends at most one blueprint per L1 level on the DAL so, to catch up, a proxy EVM node which is N L2 levels behind the sequencer needs N extra L1 levels. Since the tests relevant to the DAL usually have a sequencer 5 levels ahead, we increase the timeouts by 15 levels (from 5 to 20).

How

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR