examples: skip isochronous audio/UAC examples on CH58X

CH58x has no isochronous support (dcd_edpt_iso_alloc() returns false), but the
audio class ignores that result and the endpoints fall back to capped 64-byte
non-iso transfers, producing non-functional audio firmware. video_capture and the
FreeRTOS audio examples already carry mcu:CH58X; add it to the remaining iso
examples (audio_test, audio_4_channel_mic, audio_test_multi_rate, cdc_uac2,
uac2_headset, uac2_speaker_fb) so they are not built for CH58x.

Found by Codex review. Verified via build_utils.skip_example() that all six now
skip on ch582m_evt while control examples (e.g. cdc_msc) still build.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

examples/device/audio_4_channel_mic/skip.txt

@@ -3,3 +3,4 @@ mcu:SAME5X
 mcu:SAMG
 family:broadcom_64bit
 family:espressif
+mcu:CH58X

examples/device/audio_test/skip.txt

@@ -2,3 +2,4 @@ mcu:SAMD11
 mcu:SAME5X
 mcu:SAMG
 family:espressif
+mcu:CH58X

examples/device/audio_test_multi_rate/skip.txt

@@ -2,3 +2,4 @@ mcu:SAMD11
 mcu:SAME5X
 mcu:SAMG
 family:espressif
+mcu:CH58X

examples/device/cdc_uac2/skip.txt

@@ -6,3 +6,4 @@ mcu:SAME5X
 mcu:SAMG
 board:stm32l052dap52
 family:espressif
+mcu:CH58X

examples/device/uac2_headset/skip.txt

@@ -6,3 +6,4 @@ mcu:SAME5X
 mcu:SAMG
 board:stm32l052dap52
 family:espressif
+mcu:CH58X

examples/device/uac2_speaker_fb/skip.txt

@@ -6,3 +6,4 @@ mcu:SAME5X
 mcu:SAMG
 board:stm32l052dap52
 family:broadcom_64bit
+mcu:CH58X