v0.4.0

Breaking behavior change. The public API is unchanged — cargo semver-checks reports no
semver update required — but find_mems returns materially different results, so this takes
a minor bump under the pre-1.0 policy above rather than the patch bump an API-only check
would allow.

Fixed

• Breaking. BidirFmIndex::find_mems now enumerates MEMs in the MUMmer / BWA sense:
  a query interval is reported when at least one of its occurrences is maximal in both
  directions at that occurrence. It previously required every occurrence to be
  maximal, so a single extendable occurrence in any one reference deleted the interval.
  Both the right-maximality test (the forward loop stopped only when the occurrence set went
  empty, discarding occurrences that dropped out mid-extension) and the left-maximality test
  (rejecting the interval if any occurrence was left-extendable) were affected.

  Consequences of the old behavior: at most one interval per query start position, and a
  result set that collapsed onto find_smems, making MEM-vs-SMEM comparisons through this
  API a guaranteed null result. In a database of near-identical references, per-reference
  match recovery was systematically sparse.

  For query = ACGTACGTAC against ACGTACGTAC and ACGTACT with min_len = 2, the result
  goes from {(0,10)} to {(0,2), (0,6), (0,10), (4,10), (8,10)}.

  find_smems is unaffected and unchanged: the containment-maximal MEMs under the new
  definition are exactly the SMEMs it already returned.

Changed

• Breaking. Mem::match_count and Mem::positions from find_mems now cover only the
  maximal occurrences of a match, not every occurrence of the matched substring.
• find_mems output size is now bounded by O(|query|²) rather than |query|; min_len is the
  only guard. Expect benches/mem_bench.rs and benches/mem_positions_bench.rs timings to
  move accordingly.

Known issues

• find_mems_gpu still runs the previous whole-set algorithm and is not equivalent to
  find_mems. The shaders/mem_find.wgsl MODE_MEM port is tracked in KNOWN-ISSUES.md.