Implement endpoint read loop

[malikalhack]

Read raw data chunks from bulk endpoints in a dedicated capture thread

[malikalhack]

• Found that the DSO-2250 uses a Cypress EZ-USB FX2 chip with RAM-resident
  firmware. OldQtCode/dsoextractfw/HantekDSO.rules uploads
  DSO2250_firmware.hex and DSO2250_loader.hex through fxload on every
  USB "add" event; OldQtCode/dsoextractfw/dsoextractfw.c extracts those hex
  files from the official Windows driver (1.SYS).
• Until firmware is uploaded, the device stays in a bare bootloader state:
  no status LED activity and no working bulk endpoints. This explains the
  LED blinking seen on Windows (official driver uploads firmware
  automatically) versus no blinking on Linux with the current codebase (no
  firmware upload step exists yet, and no .hex firmware files are present
  in this repository).
• The firmware .hex files are not included because the official installer
  prohibits unauthorized redistribution; they must be extracted from a
  user's copy of the official Windows driver before the USB layer can work
  end-to-end.