Fix USB3 speed misreporting on some Apple Silicon Macs

What's fixed

Correct USB3 speed for direct-attach devices. WhatCable was reading the port controller's SuperSpeedSignaling value, which on some Apple Silicon Macs reports Gen 1 (5 Gbps) even when the device actually negotiated Gen 2 (10 Gbps). Now uses the USB host controller's Device Speed, matching what macOS System Information shows. Thanks to @janngobble for the detailed report (#140).
Hub topology handled correctly. When a USB hub is on the port, WhatCable now reads the hub's upstream link speed (the root device) instead of the fastest downstream device. This prevents overstating the port's bandwidth when a fast device sits behind a slower hub.

brew upgrade --cask whatcable, or download WhatCable.zip from this release page and drag the new .app into /Applications.