scripts: Reworked dbgbmap.py

This is a rework of dbgbmap.py to match dbgbmapd3.py, adopt the new
Rbyd/Lfs class abstractions, as well as Canvas, -k/--keep-open, etc.

Some of the main changes:

- dbgbmap.py now reports corrupt/conflict blocks, which can be useful
  for debugging.

  Note though that you will probably get false positives if running with
  -k/--keep-open while something is writing to the disk. littlefs is
  powerloss safe, not multi-write safe! Very different problem!

- dbgbmap.py now groups by blocks before mapping to the space filling
  curve. This matches dbgbmapd3.py and I think is more intuitive now
  that we have a bmap tiling algorithm.

  -%/--usage still works, but is rendered as a second space filling
  curve _inside_ the block tile. Different blocks can end up with
  slightly different sizes due to rounding, but it's not the end of the
  world.

  I wasn't originally going to keep it around, but ended up caving, so
  you can still get the original byte-level curve via -u/--contiguous.

- Like the other ascii rendering script, dbgbmap.py now supports
  -k/--keep-open and friends as a thin main wrapper. This just makes it
  a bit easier to watch a realtime bmap without needing to use watch.py.

- --mtree-only is supported, but filtering via --mdirs/--btrees/--data
  is _not_ supported. This was too much complexity for a minor feature,
  and doesn't cover other niche blocks like corrupted/conflict or parity
  in the future.

- Things are more customizable thanks to the Attr class. For an example
  you can now use the littlefs mount string as the title via
  --title-littlefs.

- Support for --to-scale and -t/--tiny mode, if you want to scale based
  on block_size.

One of the bigger differences dbgbmapd3.py -> dbgbmap.py is that
dbgbmap.py still supports -%/--usage. Should we backport -%/--usage to
dbgbmapd3.py? Uhhhh...

This ends up a funny example of raster graphics vs vector graphics. A
pixel-level space filling curve is easy with raster graphics, but with
an svg you'd need some sort of pixel -> path wrapping algorithm...

So no -%/--usage in dbgbmapd3.py for now.

Also just ripped out all of the -@/--blocks byte-level range stuff. Way
too complicated for what it was worth. -@/--blocks is limited to simple
block ranges now. High-level scripts should stick to high-level options.

One last thing to note is the adoption of "if '%' in label__" checks
before applying punescape. I wasn't sure if we should support punescape
in dbgbmap.py, since it's quite a bit less useful here, and may be
costly due to the lazy attr generation. Adding this simple check avoids
the cost and consistency question, so I adopted it in all scripts.

scripts/tracebd.py

@@ -1086,8 +1086,9 @@ if __name__ == "__main__":
             '--block-count',
             type=lambda x: int(x, 0),
             help="Block count in blocks.")
+    # TODO implies --wear?
     parser.add_argument(
-            '-c', '--block-cycles',
+            '-W', '--block-cycles',
             type=lambda x: int(x, 0),
             help="Assumed maximum number of erase cycles when measuring "
                 "wear.")
@@ -1136,7 +1137,7 @@ if __name__ == "__main__":
             action='store_true',
             help="Render erases.")
     parser.add_argument(
-            '--wear',
+            '-w', '--wear',
             action='store_true',
             help="Render wear.")
     parser.add_argument(