oans v1.6.0

Fixes a bug that silently excluded sparse files from deduplication, and changes
--exclude to .gitignore pattern syntax.

Fixes

• Sparse files whose size is not a multiple of the block size were silently
  skipped, on every run (#152). They were reported as having changed while
  being hashed — which was not true — and then dropped, so they never reached
  the hashfile and were never deduplicated. The tail of a trailing hole was
  rounded down to a block boundary, leaving a final partial block that nothing
  could read; the scan then concluded the file had changed under it and threw
  the digest away. Nothing was stored, so the next run repeated it, forever.
  This hit exactly what sparseness is used for: VM images, database files and
  preallocated media. If you have such files, this release will hash and
  deduplicate them for the first time.
• Three different conditions all reported the word "changed", with three
  different meanings and no numbers (#152). Each now states what was observed,
  the likely cause, and what follows from it — the scan-phase one in particular
  is routine on files that are still being written and now says so.
• The dedupe summary no longer reports the wrong cause. One counter was
  incremented both by our own pre-flight size check and by the kernel's
  byte-compare verdict, then printed as a single "changed since scan" figure —
  so every kernel mismatch was attributed to a file change that had not
  happened. The two are now counted and named apart.

Changes

• --exclude now uses .gitignore pattern syntax (#154, closes #147), the
  same syntax git, ripgrep and fd use:

  Pattern	Meaning
  @eaDir, *.iso	no / — matches the name at any depth
  /srv/media/cache*	leading / — absolute, anchored
  Steam/temp	interior / — matches at any depth
  cache/	trailing / — directories only
  * ? [a-z] **	* stops at /, ** crosses

  Previously patterns were matched with fnmatch() against the whole path, and
  a pattern without a leading / was resolved against the current directory —
  so --exclude node_modules matched at most one literal directory, and usually
  nothing at all, without saying so. The obvious things to write (@eaDir,
  .snapshots, node_modules) were all silent no-ops.

  This is a breaking change. Patterns already stored in a hashfile are
  replayed under the new rules, so a scheduled job may now exclude more, or
  less, than it did. Run your job once by hand and check the output before
  relying on the next timer firing. Two things make that easier: a pattern
  matching nothing is now reported as a warning (including under --quiet, so
  it reaches the journal), and a malformed pattern is an error before the scan
  starts rather than something the run ignores while scanning a wider tree.

  Negation (!) is not supported.

• --autotune has been removed (#153, closes #150). It measured hashing
  throughput at several thread counts and stored the winner in the hashfile.
  Without root it cannot drop the page cache, so it measured memory bandwidth
  instead of disk — which keeps scaling with threads well past the point where
  btrfs metadata contention caps real throughput. It printed a warning and
  persisted the answer anyway, into the hashfile a systemd timer then replays
  forever. On a 32-core NVMe machine it recommended and stored 16 threads where
  the measured plateau, and the built-in default, is 8. --io-threads is still
  sized automatically from the detected storage, and can still be set by hand.

Performance

• Exclude matching is now independent of pattern count. Patterns compile to
  a single combined PCRE2 regex with JIT enabled, rather than one fnmatch()
  per pattern per file. Measured on a 250k-file tree: ~160 ns more per file in
  the worst case (warm cache, a pattern active), around 0.5% of wall time on the
  most walk-bound workload. GLib was already a dependency, so this adds none.

Documentation

• The README is up to date with 1.4.0 and 1.5.0, and a stale hashfile-size
  figure that appeared in no benchmark has been corrected (#151).
• The NAS quick-start lost its --autotune step, and gained the upgrade note
  for the --exclude change.

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Deduplication goes through the kernel's FIDEDUPERANGE ioctl, which
byte-compares every range before sharing it.