refactor: represent slot intervals with enum

[dicethedev]

🗒️ Description / Motivation

• Replaces raw 0..4 interval dispatch in blockchain tick handling with a typed SlotInterval enum.
• This makes interval duties self-documenting and lets Rust enforce exhaustive handling when intervals change.
• Closes the gap where interval-specific behavior was matched using integer literals.

What Changed

• crates/blockchain/src/lib.rs

  • Added SlotInterval with from_slot_index as the integer slot-to-enum constructor.
  • Updated BlockChainServer::on_tick to compare and match on SlotInterval variants.
  • Kept interval logging as numeric output through Display.

• crates/blockchain/src/store.rs

  • Reused SlotInterval for the store-level tick interval match.

Correctness / Behavior Guarantees

• No behavior change intended.
• The same interval indices map to the same duties:
  • 0 → block publication
  • 1 → attestation production
  • 2 → aggregation
  • 3 → safe target update
  • 4 → end of slot
• Interval matches are now exhaustive, so adding/removing interval variants requires updating all dispatch sites at compile time.

Tests Added / Run

• No tests added; this is a refactor with no intended behavior change.
• Ran:
  • cargo fmt
  • cargo check -p ethlambda-blockchain

Related Issues / PRs

• Closes Use an enum to represent the different intervals in BlockChainServer::on_tick #469
• Related to #

✅ Verification Checklist

• Ran make fmt — clean
• Ran make lint (clippy with -D warnings) — clean
• Ran cargo test --workspace --release — all passing

[greptile-apps]

No reviewable files after applying ignore patterns.

[MegaRedHand]

If this is unused, we should just remove it

[MegaRedHand]

If possible, we should give only current time in ms -> SlotInterval and current time in intervals -> SlotInterval constructors, so that callers don't have to compute the interval themselves. That way we centralize the logic in this enum

[MegaRedHand]

Here, for example, we could do:

Suggested change

	let interval = SlotInterval::from_slot_index(
	(time_since_genesis_ms % MILLISECONDS_PER_SLOT) / MILLISECONDS_PER_INTERVAL,
	);
	let interval = SlotInterval::from_ms_since_genesis(time_since_genesis_ms);

[MegaRedHand]

And here:

Suggested change

	let interval = SlotInterval::from_slot_index(store.time() % INTERVALS_PER_SLOT);
	let interval = SlotInterval::from_intervals_since_genesis(store.time());

[MegaRedHand]

Left some comments. The direction is good, but there are some improvements I think are necessary before we merge this