v1.0.0

The stability release. The @api surface is that of 0.12.0, unchanged: no
type, method or parameter was added, removed or renamed, and a project on
^0.12 upgrades by widening the constraint to ^1.0. What the number
promises from here on is written out in the compatibility policy
(README.md, docs/src/guide/compatibility.md): the @api surface, the
corpus format (FilesystemCorpus::FORMAT_VERSION does not change within
1.x), the machine-readable keys of CounterExample::toArray() and
DistributionReport::toArray(), event fields and order, append-only
constructors — while seed → values stays outside SemVer, fenced by
FilesystemCorpus::SEQUENCE_EPOCH. The Gen::* parameter names are frozen
as they stand: $minLength/$maxLength for strings, bytes and sequences,
$minSize/$maxSize for collections, $min/$max for ranges.

• The adapters (rasuvaeff/property-testing-testo,
  rasuvaeff/property-testing-phpunit) and rasuvaeff/property-testing-names
  release their own 1.0.0 requiring this package as ^1.0, in that order
  (policy §8).
• Docs: the version gates that dated each feature (core ≥0.12,
  -testo ≥0.6, -phpunit ≥0.5, …) are gone from the skill, the guides and
  the migration document — every 1.0 install has all of them. The migration
  recipe requires -testo:^1.0.
• composer rector is green again: the three seed-hunting loops in
  CompositeArbitraryTest share one firstGenerated() helper instead of a
  nullable sentinel that FlipTypeControlToUseExclusiveTypeRector rewrote.