[noobpwnftw]

Adds chess.chesstb, a pure-Python reader for ChessTB endgame tables: WDL, DTZ, DTC, DTM and DTM50.

import chess
import chess.chesstb

with chess.chesstb.open_tablebase("/path/to/tables") as tb:
    board = chess.Board("8/8/8/5k2/8/8/1Q6/K7 w - - 0 1")
    result = tb.probe(board)  # All available metrics.
    distance = tb.probe_dtm(board)  # Signed distance from the side to move.

Tables are memory-mapped and decoded in blocks behind a shared cache. Tablebase supports concurrent probes, castling tables, opposing pawn pairs, en passant and reconstruction of omitted frames. DTC and DTM50 packs supply their embedded DTZ and DTM values when present. There are no new required dependencies; installed lz4 is used for faster WDL decoding.

Pawn-slice indexes use bitsets with the same numbering as the C++ generator. Index construction is synchronized per material. For the six-pawn opposing-pair material, construction takes 0.80 seconds instead of 151 seconds locally; the complete 152.7-million-cell bitmap and rank directory match the original implementation exactly.

Includes API documentation, fixture tables and 31 tests in ChesstbTestCase. All pass locally, including enumeration checks for pawn indexes and concurrent index construction. Existing validation against the C++ prober covered all 145 shipped materials up to five pieces, with additional checks for clocked metrics, dropped frames, loss-only tables and en passant.

ChessTB DTZ values are plain distances; unlike Syzygy's encoding, their magnitude does not carry the cursed/blessed WDL class. DTC returns (pawn pushes owed, signed plies) at the requested halfmove clock.