refactor(timeline): name the within-slot interval and drop redundant wrap (#1133)

The within-slot interval position was wrapped in an Interval only to be
unwrapped one line later in the match via int(...).
Compute the plain int once and match on it directly.
Rename it from a vague absolute-interval name to one that says it is the
position within the slot.
Behavior is identical; just check passes.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: tcoratger

src/lean_spec/spec/forks/lstar/timeline.py

@@ -21,10 +21,10 @@ def tick_interval(
     ) -> tuple[LstarStore, list[SignedAggregatedAttestation]]:
         """Advance store time by one interval and perform interval-specific actions."""
         store = store.model_copy(update={"time": store.time + Interval(1)})
-        current_interval = Interval(int(store.time) % int(INTERVALS_PER_SLOT))
+        interval_within_slot = int(store.time) % int(INTERVALS_PER_SLOT)
         new_aggregates: list[SignedAggregatedAttestation] = []
 
-        match int(current_interval):
+        match interval_within_slot:
             # Slot start: ingest pending attestations once the slot's proposal lands.
             case 0 if has_proposal:
                 store = self.accept_new_attestations(store)