Add functionality to clear stubs

src/spectator/mocks/double.cr

@@ -95,6 +95,11 @@ module Spectator
       @stubs.unshift(stub)
     end
 
+    protected def _spectator_clear_stubs : Nil
+      Log.debug { "Clearing stubs for #{_spectator_stubbed_name}" }
+      @stubs.clear
+    end
+
     private def _spectator_find_stub(call : MethodCall) : Stub?
       Log.debug { "Finding stub for #{call}" }
       stub = @stubs.find &.===(call)

src/spectator/mocks/mocked.cr

@@ -12,6 +12,10 @@ module Spectator
       _spectator_stubs.unshift(stub)
     end
 
+    def _spectator_clear_stubs : Nil
+      _spectator_stubs.clear
+    end
+
     private def _spectator_find_stub(call : ::Spectator::MethodCall) : ::Spectator::Stub?
       _spectator_stubs.find &.===(call)
     end

src/spectator/mocks/stubbable.cr

@@ -28,6 +28,9 @@ module Spectator
     # Defines a stub to change the behavior of a method.
     abstract def _spectator_define_stub(stub : Stub) : Nil
 
+    # Clears all previously defined stubs.
+    abstract def _spectator_clear_stubs : Nil
+
     # Method called when a stub isn't found.
     #
     # The received message is captured in *call*.