Check whether an implementation claim may start (#1856): at most
maxConcurrentImplementations implementations run at once (0 = no cap),
and no two live implementations share a checkout (the same directory on
the same machine; see isSameCheckout). A claim already held on the
same item is being renewed or taken over, so it never blocks itself.
Returns null when the claim may proceed.
Check whether an implementation claim may start (#1856): at most
maxConcurrentImplementationsimplementations run at once (0 = no cap), and no two live implementations share a checkout (the same directory on the same machine; see isSameCheckout). A claim already held on the same item is being renewed or taken over, so it never blocks itself. Returns null when the claim may proceed.