The `ahi_hsd` reader returns Brightness Temperatures as `float64`

[simonrp84]

The `ahi_hsd` reader returns Brightness Temperatures as `float64`

[djhoese]

Looks like this is specific to BTs:

In [2]: scn = Scene(reader="ahi_hsd", filenames=glob("/data/satellite/ahi/hsd/1830/HS_H08_20181112_1830_B*FLDK*"))

In [3]: scn.load(["B01", "B14"])

In [4]: scn["B01"].dtype
Out[4]: dtype('float32')

In [5]: scn["B14"].dtype
Out[5]: dtype('float64')

[djhoese]

Just about every scalar used in the BT calibration is a 64-bit float. Is it "the right thing to do" to cast them to 32-bit floats?