Add the ability to have tests continue to run when code under test is
reporting an error with `report_error()`.

Signed-off-by: Michael Keller <github@ike.ch>

Replace raw pointer with std::unique_ptr in TestBase::instance() singleton (#6)

Co-authored-by: mikeller <4742747+mikeller@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Signed-off-by: Michael Keller <github@ike.ch>