fix(cdc-acm): expose serial state notifications

[Oscariremma]

CDC ACM devices can report modem-state changes through an interrupt endpoint on the control interface.
This endpoint was previously left unread, which can cause some devices to stop processing subsequent USB traffic.

This PR reads CDC SERIAL_STATE notifications and exposes the reported carrier detect, data set ready, and ring indicator values through modem_status().
CTS remains unsupported because it is not part of the CDC serial-state notification.

Devices without a notification endpoint continue to return the default modem status.

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Summary by cubic

Read CDC ACM interrupt-IN serial-state notifications and expose DCD, DSR, and RI via modem_status(). Also consume and manage the control interrupt endpoint to prevent stalls and clean up on failure or close.

• New Features

  • Expose DCD, DSR, RI via modem_status() from CDC SERIAL_STATE notifications; CTS not supported.
  • Return default modem status when no notification endpoint is present.

• Bug Fixes

  • Consume the control interrupt-IN endpoint and release it/interfaces on close or init failure to avoid stalls and allow retries.
  • Validate notification payloads and surface errors from malformed frames.

^{Written for commit 72204ea. Summary will update on new commits.}

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[cubic-dev-ai]

All reported issues were addressed across 3 files

<sub>Reply with feedback, questions, or to request a fix.

Fix all with cubic | Re-trigger cubic</sub>

[s00d]

Thanks for the PR — merged.

Published as android-usb-serial 0.1.1 (plugin 3.0.2).

Follow-up on main: malformed / unrelated interrupt frames are skipped instead of killing the notification reader (same approach as usb-serial-for-android), plus wIndex filtering and padded packet support.