fix(combat): Thread 5-10-5 diagonal parity through all budget-consuming paths

The greedy move/run/flee/charge descent helpers hardcoded diagonal parity 0,
letting a speed-30 walker cover 6 diagonal cells (cell-count budget). Under
5-10-5 (SRD Movement, Tactical) the same walker covers only 4 cells
(1+2+1+2=6 squares).

Threading the running diagonal count:
- _best_move_step / _best_flee_step: accept diagonals_used param
- _descend_path / _run_line_path / _flee_path: track and pass parity
- _charge_end: use _path_cost_5105() instead of len(path) for max check
- _path_cost_5105: new helper; computes total 5-10-5 cost of any path

Updated golden paths in test_aoo_limit_one_per_round (5-cell path now
takes an orthogonal detour to avoid expensive 2nd diagonal), test_run_*
 (speed-30 diagonal move stops at 4 cells), and staggered_withdraw
(single-speed diagonal withdraw stops at 4 cells).

tests/test_conditions_effects.py

@@ -220,8 +220,9 @@ class TestStaggeredActionEconomy:
             line for line in engine._transcript if "withdraw" in line
         ]
         assert len(withdraw_lines) == 1
-        # 6 steps from (10,10) — exactly the single-speed budget.
-        assert withdraw_lines[0].count("->") == 6
+        # 4 diagonal steps from (10,10) — the single-speed budget of 6 squares
+        # under 5-10-5 (1+2+1+2=6); the old cell-count budget let it walk 6.
+        assert withdraw_lines[0].count("->") == 4
         assert h.pos != (10, 10)