usb: readable PORTSC decode, link-state names, and device string descriptors

Make the USB diagnostic logs scannable by eye:
- usb-ids gains speedName + linkStateName (USB3 PORTSC link states: U0,
  RxDetect, Polling, ...), host-tested with usb-ids.
- The PORTSC dump decodes the register instead of printing hex flags:
    PORTSC[3] 0x00021203: connected, enabled, link=U0, power=on, SuperSpeed
    PORTSC[5] 0x00020ee1: connected, disabled, link=Polling, power=on, High-speed
  (the raw word stays for reference). A USB2 device reads connected+
  disabled+Polling until reset — so the user's next log shows at a glance
  whether the companion port ever reaches that state.
- The library reads STRING descriptors (readString, UTF-16LE -> ASCII,
  English langid), and the device line now names the maker + product:
    port 5 device: Hub "Genesys Logic USB3.0 Hub" (0x05e3:0x0626), 1 interface(s)
  instead of a bare vendor/product id pair.

Full USB case set green (hub regexes follow the new 'device: <class>
"<maker> <product>"' format). Branch diagnostics for the SuperSpeed
compound-hub investigation.

test/qemu_test.py

@@ -494,7 +494,7 @@ CASES = [
      # B4a: the hub powers its ports. B4b: the keyboard behind it enumerates
      # (route string + TT) and binds usb-hid-keyboard.
      "expect": r"(?s)(?=.*hub slot \d+: \d+ downstream ports powered)"
-               r"(?=.*hub slot \d+ port \d+ device:.*vendor 0x0627)"
+               r"(?=.*hub slot \d+ port \d+ device:.*0x0627)"
                r"(?=.*usb-hid-keyboard: ok \(device 3)",
      "fail":   r"DANOS-TEST-RESULT: FAIL"},
     # USB mass storage end to end: the boot usb-storage device (the FAT32 image,
@@ -676,7 +676,7 @@ CASES = [
                     "-device", "usb-hub,bus=xhci2.0,port=1",
                     "-device", "usb-hub,bus=xhci2.0,port=1.1",
                     "-device", "usb-kbd,bus=xhci2.0,port=1.1.1"],
-     "expect": r"(?s)(?=.*hub slot \d+ port \d+ device:.*vendor 0x0409)"
+     "expect": r"(?s)(?=.*hub slot \d+ port \d+ device:.*0x0409)"
                r"(?=.*usb-hid-keyboard: ok \(device 3)",
      "fail":   r"DANOS-TEST-RESULT: FAIL"},
     # Hub-downstream disconnect (B4c): device_del the keyboard behind the hub;