Kyua 0.14: cleanup/stability release post-FreeBSD fork

Released on December 31st, 2024.

• Replace --with-atf with --enable-atf. The latter must be specified
  to enable ATF support and the Kyua tests by proxy.

• Require newer versions of ATF (0.21) and Lutok (0.5). This is being done
  as part of a multi-phase deprecation of pre-C++11 environments.

• Vendor the ATF m4 files from the freebsd/atf repo.

• Translate is_exclusive metadata to its ATF counterpart.

• Issue #236: fix accidental test forkbomb in specific user environments
  with integration tests by avoiding infinite recursion calling kyua.

• Fix the build on Ubuntu 24.04.

• execenv support added. This FreeBSD-specific feature allows tests to be
  executed in jails.

• Issue #: Remove deprecated readdir_r use.

• Fix build issue on more recent versions of MacOS.

• Fix build issue on IllumOS.

• Fix issues with PID reuse in testcases.

• Escape characters captured from stderr and stdout in HTML output.

• integration/cmd_report_test:verbose: fix regular expression used in
  tests which would break in certain user environments.

• Add Cirrus CI support for testing Kyua on FreeBSD.

• Remove UTILS_UNUSED_PARAM macro.

• Fix document rendering with newer versions of doxygen.

• Issue #152: explicitly require C++11 language features when compiling Kyua.
  Remove std::shared_ptr compatibility header, utils/shared_ptr.hpp.

• Fix igor and mandoc -Tlint reported issues with generated manpages.

• Issue #167: fix typos in kyua(1) manpage.