Remove Test::Requires dependency - prevents installation on perl 5.6
Expand the diagnostics of the spurious undefined/false $@

This augments the message to be much more descriptive, builds upon
bbaa0bac and c2f67a8c. There are no functional changes, other than
the addition of a require_module() overlay.
Switch all exceptions to Carp::croak
Test glob import as well
More sanity checks during symbol import

- Check & @ and % symbols for existence, and die if not defined.
  Skip the case of $ as it is rather cumbersome, and there isn't
  a clear solution what to do with undefined-but-aliasable scalars

- Try to load all implementations, not just the first one, and then
  make sure imported symbols exist in all of them. This was not a
  big problem until now, but the introduction of regex-based import
  lists can result in hard to track bugs without these checks
Allow wildcard import of subroutine names
Declare explicit dependency on Test::Fatal 0.006 (RT#76809)
Code style tweaks
Fix typo in test file name
Tidy all test files
Changes style tweaks