Remove some PHPStan ignores and make others rule-specific.

classes/Debug.php

@@ -77,7 +77,7 @@ class Debug {
 	 */
 	public static function map_loglevel(int $level) : int {
 		if (in_array($level, self::ALL_LOG_LEVELS)) {
-			/** @phpstan-ignore-next-line */
+			/** @phpstan-ignore return.type (yes it is a Debug::LOG_* value) */
 			return $level;
 		} else {
 			user_error("Passed invalid debug log level: $level", E_USER_WARNING);