Fix passed-pawn bitboard bit-clear bug, LMR gate coupling, inline hot bitboard helpers

- bitboard.c: CoorFromBitBoardRank1ToRank8 cleared the lowest set bit
  unconditionally instead of the reported (highest) one, silently
  mis-walking doubled-pawn files in eval.c's passed-pawn detection.
- search.c/searchsup.c: move GetLMRReduction's precondition checks from
  inside the function to the caller in search.c (pre-existing work),
  finishing the split with a matching gate in split.c's HelpSearch --
  the parallel-search call site had no gate at all, letting it call
  GetLMRReduction unconditionally (including for checking moves),
  reachable only under real multithreading (--cpus > 1) and the
  intermittent root cause of assertion crashes seen under --cpus 4.
- eval.c: redirect CountBits/CoorFromBitBoardRank8ToRank1/
  CoorFromBitBoardRank1ToRank8 to inline compiler-builtin versions
  (gated !CROUTINES) instead of the real out-of-line asm calls, on
  eval.c's ~20 existing production call sites. CountBits' asm body
  isn't O(1) popcnt, it's a Kernighan bit-clearing loop plus call
  overhead, paid on every Eval() call.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Jntky4yGUTyQVaGCXms4F2

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