Prepare for 0.016 release

[jkeenan]

This merge request prepares for the 0.016 release of Test-Vars. It does so primarily by adapting the configure/build/test/release cycle needed for a CPAN release to the exigencies of the status of Perl 5 in late August/early September 2024.

In monthly development release perl-5.41.3 saw several changes in which long deprecated code was removed from the language. These removals included the elimination of the apostrophe (') from package and variable names and the deprecation of the given/when/switch functionality and the smartmatch (~~) operator. As a consequence, many CPAN distributions are failing to build or experiencing test failures on CPANtesters. (See, e.g., Perl/perl5#22517 and Perl/perl5#22524.)

While Test-Vars was not directly impacted by these changes, its "authoring" system, which might best be described as "Minilla wrapping around Module-Build-Tiny," was. Minilla has an indirect dependency on CPAN library common-sense, which was broken by the smartmatch removal and which is not likely to be repaired soon. Here's what you get if you try to use cpan to install Minilla against blead perl today:

Failed during this command:
 (optional) MLEHMANN/common-sense-3.75.tar.gz : make NO
 MLEHMANN/Types-Serialiser-1.01.tar.gz        : make_test NO one dependency not OK (common::sense); additionally test harness failed
 (optional) MLEHMANN/JSON-XS-4.03.tar.gz      : make_test NO 2 dependencies missing (Types::Serialiser,common::sense); additionally test harness failed
 KARUPA/TOML-Parser-0.91.tar.gz               : make_test NO one dependency not OK (Types::Serialiser); additionally test harness failed
 KARUPA/TOML-0.97.tar.gz                      : make_test NO one dependency not OK (TOML::Parser); additionally test harness failed
 SKAJI/Minilla-v3.1.25.tar.gz                 : make_test NO one dependency not OK (TOML); additionally test harness failed

What Is To Be Done?

Test-Vars has mostly been failing on CPANtesters for the past two years. If we've repaired its code deficiencies -- which we have in the master branch -- then we should by trying to get it to CPANtesters and CPAN as soon as possible. We should work around any problems its build system is experiencing that are outside of our immediate control.

To that end, I have replaced Module::Build::Tiny in the build system with ExtUtils::MakeMaker. This entailed replacing Build.PL with Makefile.PL and incorporating the guts of cpanfile by bringing its data into Makefile.PL. (I would have considered using Module::Build, but it's no longer shipped with the Perl core distribution and my CPAN-maintenance philosophy calls for elimination of unnecessary dependencies and needless complexities.) I believe that my Makefile.PL is highly compliant with the documentation for ExtUtils::MakeMaker and CPAN::Meta::Spec. (I've added an author-only test, xt/05_test-meta.t, to validate the metadata.) I have enough experience with EU::MM and make to be able to add make targets, so I've added make test_author and alias make atest for ease in further testing. I've made several development releases which are doing well on CPANtesters.

Assuming CPANtesters continues to go green, I intend to merge this p.r. into master no later than Saturday, September 14. I will then review and update the documentation in lib/Test/Vars.pm, update Changes, bump the version number and release to CPAN no later than Thursday, September 19 (in order to be able to take advantage of CPANtesters runs after the monthly Perl dev release scheduled for Sept. 20).