feat(tusb_msc): Add device mount/unmount callback

[peter-marcisovsky]

Description

This MR adds a possibility to define a user callback for device mount/unmount events.

Right now, the tusb_msc_storage.c automatically calls:

• tinyusb_msc_storage_mount() at tud_umount_cb()
• tinyusb_msc_storage_unmount() at tud_mount_cb()

User has no flexibility to do anything else upon the device mount/unmount.

This MR adds a flexibility to the user, to for example control an owership of the storage (eg, not to automatically unmount a storage when a USB device is plugged in)

Also cleaned conceptions between device mount/unmount and storage mount/unmount, not to confuse anyone when the code refers to device mount/unmount and when to storage mount/unmount.

Related

Related to #78

Testing

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Checklist

Before submitting a Pull Request, please ensure the following:

• 🚨 This PR does not introduce breaking changes.
• All CI checks (GH Actions) pass.
• Documentation is updated as needed.
• Tests are updated or added as necessary.
• Code is well-commented, especially in complex areas.
• Git history is clean — commits are squashed to the minimum necessary.

[peter-marcisovsky]

I added a user callback which gets called at tud_umount_cb() or tud_mount_cb().

There is a new event TINYUSB_MSC_EVENT_DEVICE_MOUNT_CHANGED registered to the callback looking like this:

typedef enum {
    TINYUSB_MSC_EVENT_MOUNT_CHANGED,                /*!< Event type AFTER storage mount/unmount operation is successfully finished */
    TINYUSB_MSC_EVENT_PREMOUNT_CHANGED,             /*!< Event type BEFORE storage mount/unmount operation is started */
    TINYUSB_MSC_EVENT_DEVICE_MOUNT_CHANGED,         /*!< Event type at device mounted/unmounted event */
} tinyusb_msc_event_type_t;

There are 3 events now, EVENT_MOUNT, EVENT_PREMOUNT and EVENT_DEVICE_MOUNT.
It might make sense to rename:

• EVENT_MOUNT to EVENT_STORAGE_MOUNT
• EVENT_PREMOUNT to EVENT_STORAGE_PREMOUNT

Just to make sure, which event is registered to storage mount and which to device mount. So we will have something like this:

typedef enum {
    TINYUSB_MSC_EVENT_STORAGE_MOUNT_CHANGED,                /*!< Event type AFTER storage mount/unmount operation is successfully finished */
    TINYUSB_MSC_EVENT_STORAGE_PREMOUNT_CHANGED,             /*!< Event type BEFORE storage mount/unmount operation is started */
    TINYUSB_MSC_EVENT_DEVICE_MOUNT_CHANGED,         /*!< Event type at device mounted/unmounted event */
} tinyusb_msc_event_type_t;

But those event enums are used in tusb_msc example So we will be changing some publicly accessible enums. Also esp-idf examples build CI Job won't pass.

What do you think?