[Chess] Reduce _is_checked call

[sotetsuk]

c.f. #1230

fn	jaxpr lines	time
_legal_action_mask	2467	728.2ms
_flip	92	33.4ms
_is_checked	206	68.8ms
_is_pseudo_legal	136	40.4ms
_hash_castling_en_passant	37	18.5ms
_apply_move	331	107.0ms
_update_history	57	30.9ms

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.58%. Comparing base (8760db1) to head (6106755).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1231      +/-   ##
==========================================
- Coverage   80.64%   80.58%   -0.06%     
==========================================
  Files          62       62              
  Lines        5967     5950      -17     
==========================================
- Hits         4812     4795      -17     
  Misses       1155     1155              

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