expose bootloader_version in device info #138

Firmware's optional DeviceInfoResponse.bootloader_version reports the marketing
version of the installed stage1 bootloader. Expose it as Option<String> in the
result of device_info(), preserving None when firmware does not report it
(including legacy bootloaders).

The field is missing from master. Copy the protobuf definitions from
bitbox02-firmware and regenerate the Rust bindings.

The protobuf update in #137 already implements this; tracking here until it is merged.