v0.1.4

Cooperative walk cancellation and one PGN game splitter, both driven by the
BlindBase live-set position search: a 50-game answer over an 11M-game set no
longer costs a full decode.

Added

• GameSink::cancelled (default false), polled per record by
  for_each_game / for_each_range and per wave by convert_parallel.
  A cancelled run returns its prefix stats with ConvertStats::complete = false,
  mirroring PositionSearch::complete — a prefix is never mistaken for a whole answer.
• cbvault::pgn::split (split_games, split_game_ranges): the one
  boundary rule (blank line outside a comment whose next non-blank line is a
  tag pair), byte-based with lossy UTF-8, ported from BlindBase with its test
  vectors. The rule has one owner now so both sides of the bridge split the
  same bytes the same way.

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Full Changelog: v0.1.3...v0.1.4