Follow-up: TT instrumentation test coverage and additional code paths

[wopdevries]

Follow-up to #365 (TT hit-rate instrumentation).

Remaining Copilot review comments to address:

1. TransTableS instrumentation — DDS_TT_KIND=small always reports adds=0/overwrites=0; instrument or label as unavailable
2. Unit tests for ab_search.cpp counters — assert hit/miss counts and per-solve reset in existing TT lookup tests
3. Unit tests for TransTableL op stats — test insertion, full-block replacement, and reset_op_stats()
4. analyse_later_board path — AnalysePlayBin reuses the same context; add reset/report lifecycle or scope feature to solve_board/solve_same_board only

These were deferred from #365 to keep that PR focused on basic instrumentation.