Rust tools for working with Realtek firmware

Further adventures in porting tools to Rust to flesh out the supported
API.

These tools didn't feel like `example`s, so I made a top level `bumble`
CLI tool that hosts them all as subcommands. I also moved the usb probe
not-really-an-`example` into it as well. I'm open to suggestions on how
best to organize the subcommands to make them intuitive to explore with
`--help`, and how to leave room for other future tools.

I also adopted the per-OS project data dir for a default firmware
location so that users can download once and then use those .bin files
from anywhere without having to sprinkle .bin files in project
directories or reaching inside the python package dir hierarchy.

tools/rtk_fw_download.py

@@ -67,8 +67,9 @@ def download_file(base_url, name, remove_suffix):
 @click.command
 @click.option(
     "--output-dir",
-    default=".",
-    help="Output directory where the files will be saved",
+    default="",
+    help="Output directory where the files will be saved. Defaults to the OS-specific"
+    "app data dir, which the driver will check when trying to find firmware",
     show_default=True,
 )
 @click.option(
@@ -84,7 +85,10 @@ def main(output_dir, source, single, force, parse):
     """Download RTK firmware images and configs."""
 
     # Check that the output dir exists
-    output_dir = pathlib.Path(output_dir)
+    if output_dir == '':
+        output_dir = rtk.rtk_firmware_dir()
+    else:
+        output_dir = pathlib.Path(output_dir)
     if not output_dir.is_dir():
         print("Output dir does not exist or is not a directory")
         return

tools/rtk_util.py

@@ -61,9 +61,8 @@ async def do_load(usb_transport, force):
         # Get the driver.
         driver = await rtk.Driver.for_host(host, force)
         if driver is None:
-            if not force:
-                print("Firmware already loaded or no supported driver for this device.")
-                return
+            print("Firmware already loaded or no supported driver for this device.")
+            return
 
         await driver.download_firmware()