DAL/Proto: introduce & plug a dynamic case for attestation_lag_kind

For deps, see https://docs.google.com/spreadsheets/d/1rak6nBXnlNggnOnA5WTF7idHNXn0hsSCnVqrypHBew0/edit?usp=sharing

Handled item from original MR !19500 (merged):

2. Enable alternate lag (internal): the ability to have a different lag than the legacy one, still not user-exposed.
3. Plug the ability to provide the lag from outside (i.e., when calling cell addition functions).

What changes

• Type: attestation_lag_kind = Legacy | Dynamic of int

• Encoding: add new dynamic cases for cell content (unpublished_dyn/published_dyn) so that:

• Legacy cells keep identical bytes/hashes (backward compatible).

• Dynamic n cells serialize n and thus commit to it in the cell hash.

• APIs: extend

• Slots_history.update_skip_list[_no_cache] ... ~attestation_lag

• Storage wrapper and caller to update_skip_list now pass Dynamic attestation_lag, where attestation_lag os taken from protocol constants.

• Tests: updated to provide ~attestation_lag:Legacy. We could provide Dynamic lag, when the lag is known as well.

Compatibility guarantees

• No behavior change for existing data: legacy cells decode as Legacy, are re-serialized identically.
• New cells can be produced with Dynamic n (currently fed from constants), but no external config exposed yet.
• The use of Dynamic legacy_attestation_lag should guarantee the same semantics and behaviour (skip-list shape, refutation proofs, ...) as using Legacy