I was testing Optimization Detective and I was confused why it wasn't working. Pages which normally had been optimized were being served as if Optimization Detective wasn't even active. It turns out that this is a side effect of #1762 where we prevent any page processing when the REST API for storing URL Metrics is unavailable. Since loopback requests don't work in wp-env (WordPress/gutenberg#20569), neither does the Site Health test for checking whether the REST API is available.

Without the patch in this PR, a plugin can force optimization to apply even when the REST API isn't available via code like the following:

// The wp-env environment does not support loopback requests, so we need to pretend that everything is good.
add_filter(
	'pre_option_od_rest_api_unavailable',
	static function ( $pre ): string {
		if ( ! is_admin() ) {
			return '0';
		}
		return $pre;
	}
);

This could be added to the od-dev-mode plugin. But this plugin shouldn't have to be installed in order to test Optimization Detective in wp-env.

So this PR adds a condition (a7cedce) so that od_is_rest_api_unavailable() is checked alongside ( wp_get_environment_type() !== 'local' || class_exists( 'Test_OD_Optimization' ) ). Only if both are true will it short-circuit.

Additionally, to assist with helping users understand why Optimization Detective isn't doing anything, this PR includes the reasons for optimization being disabled in the console when WP_DEBUG is enabled.