refactor(state-transition): simplify slot increment and module docstring (leanEthereum#1103)

Drop the redundant Slot() wrapper around an already-Slot sum, and
shorten the module header to a single plain summary line.

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

Author: tcoratger

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

@@ -1,4 +1,4 @@
-"""Lstar fork — state transition: slots, header, body, finalization."""
+"""Lstar fork — state transition."""
 
 from collections.abc import Iterable
 from typing import Any
@@ -96,7 +96,7 @@ def process_slots(self, state: State, target_slot: Slot) -> State:
                     "latest_block_header": state.latest_block_header.model_copy(
                         update={"state_root": cached_state_root}
                     ),
-                    "slot": Slot(state.slot + Slot(1)),
+                    "slot": state.slot + Slot(1),
                 }
             )