usb-device-mtp: Add MTP device driver for MicroPython filesystem.

Implements a Media Transfer Protocol (MTP) device driver that exposes
the MicroPython filesystem to USB hosts. This allows accessing files
on the device via standard file managers without requiring special tools.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: andrewleech

micropython/usb/examples/device/mtp_example.py

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+# MicroPython USB MTP example
+#
+# This example demonstrates creating a USB MTP device to expose the MicroPython
+# filesystem to a host computer.
+#
+# To run this example:
+#
+# 1. Make sure `usb-device-mtp` is installed via: mpremote mip install usb-device-mtp
+#
+# 2. Run the example via: mpremote run mtp_example.py
+#
+# 3. mpremote will exit with an error after the previous step, because when the
+#    example runs the existing USB device disconnects and then re-enumerates with
+#    the MTP interface present. At this point, the example is running.
+#
+# 4. To see output from the example, reconnect: mpremote connect PORTNAME
+#
+# 5. On your host computer, you should see a new storage device appear that
+#    allows browsing the MicroPython's filesystem.
+#
+# MIT license; Copyright (c) 2024 MicroPython Developers
+import usb.device
+from usb.device.mtp import MTPInterface
+import time
+
+# Create an MTP interface that exposes the root directory
+mtp = MTPInterface(storage_path="/")
+
+# Initialize the USB device with the MTP interface
+# Keep builtin_driver=True to maintain the serial REPL alongside MTP
+usb.device.get().init(mtp, builtin_driver=True)
+
+print("Waiting for USB host to configure the MTP interface...")
+
+# Wait for the host to configure the interface
+while not mtp.is_open():
+    time.sleep_ms(100)
+
+print("MTP interface is now available to the host.")
+print("Your MicroPython filesystem should be accessible on the host computer.")
+print("Press Ctrl+C to exit.")
+
+# Keep the script running
+try:
+    while True:
+        time.sleep(1)
+except KeyboardInterrupt:
+    print("MTP example terminated by user.")

micropython/usb/usb-device-mtp/__init__.py

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+# MicroPython USB MTP package
+# MIT license; Copyright (c) 2024 MicroPython Developers
+from usb.device.mtp import MTPInterface

micropython/usb/usb-device-mtp/manifest.py

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+# MicroPython package manifest for usb-device-mtp
+package(
+    "usb-device-mtp",
+    (
+        "__init__.py",
+        "usb/device/mtp.py",
+    ),
+    base_path="..",
+    version="1.0.0",
+    description="USB MTP device driver for MicroPython",
+    url="https://github.com/micropython/micropython-lib",
+    license="MIT",
+    author="MicroPython Developers",
+    author_email="team@micropython.org",
+)
+
+requires("usb-device")