use NBITS=16 when saving LOS files

[scottstanie]

In [5]: fn = 'los_east.tif'
In [6]: r1 = io.load_gdal(Path("current") / fn); r2 = io.load_gdal(Path("nbits16") / fn)

# Largest difference between `main` and new version
In [7]: np.max(np.abs(r1 - r2))
Out[7]: 0.00048828125

# relative error:
In [10]: np.max(np.abs(r1 - r2)) / np.max(np.abs(r1))
Out[10]: 0.00068804994

New version is ~1/4 the size for the LOS files

(mapping-311) staniewi:opera-utils$ ls -lh l*tif current/
-rw-r--r--  1 staniewi  staff   156K Jul 15 21:50 layover_shadow_mask.tif
-rw-r--r--  1 staniewi  staff   1.3M Jul 15 21:50 los_east.tif
-rw-r--r--  1 staniewi  staff   1.5M Jul 15 21:50 los_north.tif
(mapping-311) staniewi:opera-utils$ ls -lh nbits16/
total 1672
-rw-r--r--  1 staniewi  staff   156K Jul 15 20:45 layover_shadow_mask.tif
-rw-r--r--  1 staniewi  staff   350K Jul 15 20:45 los_east.tif
-rw-r--r--  1 staniewi  staff   328K Jul 15 20:45 los_north.tif