v0.5.2

• Requires rasuvaeff/understudy ^0.9 || ^0.10. The engine's 0.10 closes six
  defects of the 1.0 review, the widest of them being that an optional
  parameter no longer has to be spelled in a specification: when(fn () => $repository->find(1)) now matches a contract whose remaining parameters
  carry defaults, and an unspelled position is rendered as … in reports so
  it is never mistaken for a written any(). Nothing this extension does changes
  — the arity suppression it carries is about Arg::rest(), which still
  covers the contract's required parameters and only those.
• Drops the ^0.8 term, as 0.5.1 said it would in the release that
  follows the engine's.