refactor(types): move the interval grid into ethlambda-types

[MegaRedHand]

🗒️ Description / Motivation

Extracted from #561, which needs the interval grid readable from ethlambda-storage. The move stands on its own, so it lands here rather than riding along with the heartbeat work.

ethlambda-storage derives slot and interval from store.time(), but it cannot depend on ethlambda-blockchain — the dependency runs the other way. Today it can only document the formula in a comment on Store::time() instead of using the constants. ethlambda-types is already a dependency of both crates, so housing them there removes the asymmetry and keeps a second copy of a consensus-critical constant from appearing in storage.

What Changed

• crates/common/types/src/constants.rs — now defines MILLISECONDS_PER_INTERVAL, INTERVALS_PER_SLOT and MILLISECONDS_PER_SLOT, docs carried over verbatim.
• crates/blockchain/src/lib.rs — the three definitions become a re-export of the same names from ethlambda_types::constants.

Correctness / Behavior Guarantees

Pure move. Values are unchanged: 800 ms per interval, 5 intervals per slot, 4000 ms per slot.

ethlambda_blockchain::{MILLISECONDS_PER_INTERVAL, INTERVALS_PER_SLOT, MILLISECONDS_PER_SLOT} still resolve via the re-export, so no downstream import changes — crates/net/rpc/src/spec.rs in particular is untouched.

tooling/event-monitor keeps its own DEFAULT_INTERVALS_PER_SLOT; it is a separate binary that reads the real value from /lean/v0/config/spec over HTTP and only falls back to the local default when no node answers.

Tests Added / Run

No new tests — there is no behavior to test. Existing suite covers the constants through every consumer.

make fmt
make lint
make leanSpec/fixtures     # fixtures were absent in the worktree
cargo test --workspace --profile release-fast --no-fail-fast

Related Issues / PRs

• Extracted from feat(consensus): two-tier heartbeat fork choice on a 4-interval slot #561

✅ Verification Checklist

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

[greptile-apps]

Greptile Summary

This PR moves the consensus interval-grid constants into the shared ethlambda-types crate while preserving the existing ethlambda-blockchain API through re-exports.

• Defines the 800 ms interval, five intervals per slot, and derived 4000 ms slot duration in ethlambda_types::constants.
• Re-exports all three constants from ethlambda_blockchain so existing consumers require no import changes.

Confidence Score: 5/5

The PR appears safe to merge because it preserves both the timing values and the existing public import paths.

The shared constants module is public, blockchain already depends on the types crate, and the re-exported constants retain their original names, u64 types, and values.

Important Files Changed

Filename	Overview
crates/blockchain/src/lib.rs	Replaces local timing constants with transparent public re-exports of the same names, types, and values.
crates/common/types/src/constants.rs	Adds the unchanged interval-grid constants to the shared types crate without affecting serialized types or consensus data layouts.

_{Reviews (1): Last reviewed commit: "refactor(types): move the interval grid ..." | Re-trigger Greptile}