Ruby 3.0 does not include Coverage.setup

[mschwager]

For reasons related to #9, Ruzzy requires calling Coverage.setup for its coverage support:

ruzzy/ext/cruzzy/cruzzy.c

Lines 195 to 211 in 0f554e6

	static void enable_branch_coverage_hooks()
	{
	// Call Coverage.setup(branches: true) to activate branch coverage hooks.
	// Branch coverage hooks will not be activated without this call despite
	// adding the event hooks. I suspect rb_set_coverages must be called
	// first, which initializes some global state that we do not have direct
	// access to. Calling setup initializes coverage state here:
	// https://github.com/ruby/ruby/blob/v3_3_0/ext/coverage/coverage.c#L112-L120
	// If rb_set_coverages is not called, then rb_get_coverages returns a NULL
	// pointer, which appears to effectively disable coverage collection here:
	// https://github.com/ruby/ruby/blob/v3_3_0/iseq.c
	rb_require("coverage");
	VALUE coverage_mod = rb_const_get(rb_cObject, rb_intern("Coverage"));
	VALUE hash_arg = rb_hash_new();
	rb_hash_aset(hash_arg, ID2SYM(rb_intern("branches")), Qtrue);
	rb_funcall(coverage_mod, rb_intern("setup"), 1, hash_arg);
	}

Unfortunately, Coverage.setup was not added until Ruby 3.1.0:

• https://bugs.ruby-lang.org/issues/18176
• https://rubyreferences.github.io/rubychanges/3.1.html

Notably, Ubuntu 22.04 is still using Ruby 3.0.X. Coverage.start is available in 3.0, and should achieve the same effect. We need to either unconditionally call Coverage.start, or find a way to conditionally call start vs. setup, and test that this works on Ubuntu 22.04.