eval.c: bad-trades fix, rook cache, xColor speedups, draw scaling, main-body reorder

Continues re-applying the eval.c overhaul from stash@{0} (see fbb138c),
each piece verified individually against clean 434fa04 (fast st1 matches,
~30-40 games each) before landing:

- _EvalBadTrades: replaced the TRADE_PIECES/DONT_TRADE_PAWNS lookup
  tables with direct arithmetic (part of a broader "eval.c is too slow,
  cut lookup tables where possible" effort). The stash's first attempt
  at this had a real bug: uInverseBehindPieceCount was computed by
  subtracting a raw material sum from 9 in unsigned arithmetic, which
  underflows to ~4 billion in any non-bare-endgame position with
  unequal material -- confirmed via match_play (score 0.15-0.225 over
  20 games vs clean 434fa04, a near-total wipeout). Fixed to use the
  existing uNonPawnCount piece-count field directly instead of
  reinventing it via material math, and restored a cheap zero-pawn
  guard (old DONT_TRADE_PAWNS punished "material lead with zero pawns
  left" specifically -- the classic KNB-vs-KRP false positive -- which
  the arithmetic replacement had dropped entirely). Verified back at
  parity (0.475/40 games) after the fix.
- _EvalRook: ROOK_FULL_HALF_OPEN_BONUS is now a startup-computed cache
  (InitEval(), refreshed on every DNA reload) instead of a per-call
  local array rebuild.
- xColor = FLIP(uColor) cached once instead of recomputed inline:
  _EvalBishop, _EvalKnight, CountKingSafetyDefects (also renamed its
  uSide/xSide params to uColor/xColor to match), and Eval()'s own
  per-piece-type loop.
- _EvalBishopPairs collapsed to one FOREACH_COLOR loop instead of
  duplicated per-side code.
- eval.c "diet" cleanup: removed pos->iTempScore (a scalar handoff
  between _EvalKing and Eval()'s per-color copy, now redundant --
  _EvalKing writes directly into ctx->sPlyInfo[ply].iKingScore[uColor]);
  removed several stale comments documenting already-historical
  removals; _EvalPassers renamed to _ReEvalPassers; re-enabled a
  previously-disabled ASSERT in _EvaluateCandidatePasser (confirmed
  live via DEBUG smoke test, does not fire under current DNA).
- Added _SideHasWinningChances (Crafty-style material-only "can this
  side force a win at all" classifier) plus the fifty-move-rule
  dampening in Eval() -- both scale the score toward g_iDrawScore when
  material alone rules out real winning chances, without touching
  Eval()'s signature (kept the existing scalar piPositional convention
  rather than pulling in the super-lazy exit's per-color rework).
- Removed the "B over N in the endgame with 2 pawn wings" term
  entirely, by direct instruction -- BISHOP_OVER_KNIGHT_IN_ENDGAME is
  now an orphaned DNA constant (matches the stash's own choice, which
  left it similarly unused).
- Eval()'s main per-piece-type loop reordered from "all of our minors,
  then all of the enemy's minors, then rooks both colors, then queens
  both colors" to "ours then enemy's, interleaved per type" (knights,
  then bishops, then rooks, then queens). Verified the real dependency
  this ordering has to preserve -- _EvalRook/_EvalQueen read the
  enemy's bbMinorAttacks, _EvalKing reads both colors' bbMinorAttacks/
  bbQueenAttacks, _ReEvalPassers needs the king scores -- and confirmed
  the new interleaving still satisfies it (all minors both colors done
  before any rook/queen; both colors done before king).

Verification methodology throughout: gmake clean release build, DEBUG
smoke test (10 random ECM positions at sd 5, asserts compiled in), then
a fast (st 1, 40-game) match_play.py run against a clean 434fa04
reference binary before landing each piece. A same-binary-vs-itself
control match (score 0.500/20 games) confirms the harness itself has no
structural bias, so per-checkpoint scores in the 0.44-0.58 band across
this session reflect real (if noisy) parity, not measurement artifacts.

Still not re-applied (remains in stash@{0}): the super-lazy exit, the
material-based normal-lazy floor, and search.c's qsearch futility
rework -- these three are one coupled unit (the futility margins index
by which Eval() exit tier fired) and go in as the next, more carefully
scrutinized step, since the original regression that started this
whole investigation traced to exactly this area.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Ka9o3S2eKqh4jNfmxVZ6fH

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