mux: wire TrueHD channel probe into iso:// mux setup

correct_truehd_channels() probes the first DECRYPTED access units of the
chosen title (TrueHD PIDs, bounded 8 MiB read of the first extent) and
sets AudioStream.channels from the MLP major sync — fixing the MPLS
audio_format understatement (5.1 declared on a 7.1/Atmos TrueHD track).
Regenerates the basic codec label for the corrected count; richer
editorial labels are left untouched. Wired in resolve.rs input() for
iso:// after decrypt_with (the m2ts is only decryptable post-key), using
a fresh reader so the mux reader is undisturbed. generate_audio_label
made pub(crate).

src/labels/mod.rs

@@ -412,7 +412,7 @@ fn codec_hint_adds_detail(hint: &str) -> bool {
     h.contains("atmos") || h.contains("dts:x") || h.contains("dts-x") || h.contains("dtsx")
 }
 
-fn generate_audio_label(
+pub(crate) fn generate_audio_label(
     codec: &crate::disc::Codec,
     channels: &crate::disc::AudioChannels,
     _secondary: bool,