v0.5.1

• Allows rasuvaeff/understudy ^0.8 || ^0.9. A bridge, not a widening for
  its own sake: the engine's 0.9 is the 1.0 candidate — every contract decision
  of the 1.0 review lands there, and 1.0 follows once it has been driven by real
  packages — and a project taking it must be able to keep this extension without a
  window in which composer require silently installs the 0.8 engine beside
  it. The ^0.8 term is dropped in the release that follows the engine's.
• understudy.returns is reported past the first link of the chain.
  when(fn () => $gate->close())->times(2)->returns(null) and
  ->throws(…)->then()->returns(null) on a void method were silent while
  the direct form was reported: the rule read only the immediate receiver of
  returns(), found a MethodCall there and gave up — the blindness
  FluentCardinalityRule had for times() until 0.5.0. It walks the chain
  down to the verb now. Fixes #31.
• Rector is green again, which it had not been since 0.3.0: rector.php
  skips the fixture projects — they are the test input, and
  SortCallLikeNamedArgsRector would have rewritten the Misuse fixture
  that pins named bounds in either order into the order that never showed the
  bug — and the remaining suggestions are applied. composer release-check
  is what gates a tag, and it had been red under green builds.
• infection/infection moves to ^0.35, the monorepo's single-major form.
• Documentation no longer dates the Arg::rest() and Arg::captor() idioms to
  «understudy 0.4»: with a floor of ^0.8 every engine this package installs
  beside has them.