internal/pipewire: implement Core::Done

The message in the sample does not correspond to any known method call. The spec does not mention what to do with messages like this, but all existing usage code simply drops it.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pipewire/header_test.go

@@ -65,6 +65,12 @@ func TestHeader(t *testing.T) {
 			Size:   0x7d0, Sequence: 4, FileCount: 0,
 		}, nil},
 
+		{"PW_CORE_EVENT_DONE", []byte(recvmsg00Message05Header), pipewire.Header{
+			ID:     pipewire.PW_ID_CORE,
+			Opcode: pipewire.PW_CORE_EVENT_DONE,
+			Size:   0x58, Sequence: 5, FileCount: 0,
+		}, nil},
+
 		{"PW_SECURITY_CONTEXT_METHOD_CREATE", []byte{
 			// Id
 			3, 0, 0, 0,