Cherry-pick non-LMR fixes and tooling from the "LMR" stash

Pulled the parts of the stashed LMR work that are genuinely independent
of the reduction logic itself, leaving the actual LMR redesign for
separate review:

- Fix extension-taper table overflow: remove the flat MAX_EXTEND_PER_LINE
  cap and instead clamp the depth used to build g_uExtensionReduction[]
  so a deep `sd` request can't leave the whole taper table stuck at "0
  penalty" (every index unreachable).
- Remove a spuriously-firing ASSERT(fMovesRescoredByIID) in Search():
  RescoreMovesViaSearch's own fail-high branch deliberately leaves that
  flag FALSE by contract, so the assert could fire on any DEBUG build
  given an unlucky rescore, making the DEBUG/TEST harness unreliable.
- Misc correctness/portability fixes: unix.c pointer-truncation casts,
  chess.h's CONTAINING_STRUCT/IS_ENPASSANT/ABS_DIFF macro hardening
  (plus gating the branchless bit-tricks on _X64_ too, not just _X86_),
  removal of dead Slide*WithoutSigs prototypes, main.c's hash default
  bumped to 256m and its CPP self-test's arch gate widened to _X64_.
- eval_tune/match_play.py: cosmetic SPRT progress-bar/output rework.
- Delete eval_tune/run_ecm.sh (superseded, unreferenced elsewhere).
- run_tests.sh: parameterize suites/SD/SN via args/env vars instead of
  hardcoding the three curated suites and sd10/sn5M (defaults kept
  pointing at the existing curated suites, since the stash's own
  lmr_sensitive_30/lmr_control_30 default suites aren't present in the
  repo).

Deliberately left out of this commit: the stash's actual LMR reduction
logic, the M-SIGNAL-SHADOW diagnostic subsystem, the large PERF_COUNTERS
instrumentation buildout, the history-table gravity rework, and the
FindEnprisePiece pre-move staleness fix (skipped per request pending a
decision on whether to also change EFP's pruning behavior).

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01MjdDfHry3i2jfJzyDXaG8A

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