Bound automatic diagonal heuristics by two cardinal steps

[antonsoo]

SimpleGraph can overestimate the remaining cost when a diagonal costs more than two cardinal steps. On the regression's unit-cost map, cardinal cost 1 and diagonal cost 3 return a cost-9 path although eight cardinal steps suffice.

Cap the automatic diagonal estimate at two cardinal steps. Keep the actual diagonal edge cost, diagonal-only graphs, greed multiplier and explicit heuristic overrides.

The regressions cover C/F layouts and diagonal-only movement. An independent sample-dungeon heap oracle confirms all 60 previously incorrect single-endpoint queries, with all 1,920 ordinary-cost controls unchanged. A separate many-to-many reconstruction correction handles the remaining 59 failures; both together match all 2,240 queries.

Full headless tests pass (324 passed, 95 skipped), using pinned native resource assets and SDL dummy audio. Mypy and applicable project formatting/hooks pass.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.09%. Comparing base (84dd3bb) to head (76bda52).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #198   +/-   ##
=======================================
  Coverage   86.09%   86.09%           
=======================================
  Files          29       29           
  Lines        7597     7597           
=======================================
  Hits         6541     6541           
  Misses       1056     1056           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.