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.

system/devices/usb-ids.zig

@@ -103,6 +103,38 @@ pub fn className(class: u8) []const u8 {
     };
 }
 
+/// The USB speed class (as xHCI reports it in PORTSC/slot contexts) named.
+pub fn speedName(speed: u32) []const u8 {
+    return switch (speed) {
+        1 => "Full-speed",
+        2 => "Low-speed",
+        3 => "High-speed",
+        4 => "SuperSpeed",
+        5 => "SuperSpeedPlus",
+        else => "unknown-speed",
+    };
+}
+
+/// A USB3 Port Link State (xHCI PORTSC PLS field) named.
+pub fn linkStateName(pls: u32) []const u8 {
+    return switch (pls) {
+        0 => "U0",
+        1 => "U1",
+        2 => "U2",
+        3 => "U3-suspended",
+        4 => "Disabled",
+        5 => "RxDetect",
+        6 => "Inactive",
+        7 => "Polling",
+        8 => "Recovery",
+        9 => "HotReset",
+        10 => "Compliance",
+        11 => "Test",
+        15 => "Resume",
+        else => "reserved",
+    };
+}
+
 /// A fuller name for a HID interface's (subclass, protocol): "HID boot keyboard"
 /// / "HID boot mouse", else just the class name. Used to make input devices
 /// recognizable in logs.