FIX: Fix type of time for odim reader

[mgrover1]

• Closes BUG: read_odim_hdf5 - TypeError: 'numpy.float32' object cannot be interpreted as an integer #1408
• Documentation reflects changes

[mgrover1]

@zssherman before we merge, I want to test with the file included in the issue

[mgrover1]

Things are working as expected:

In [1]: import pyart

## You are using the Python ARM Radar Toolkit (Py-ART), an open source
## library for working with weather radar data. Py-ART is partly
## supported by the U.S. Department of Energy as part of the Atmospheric
## Radiation Measurement (ARM) Climate Research Facility, an Office of
## Science user facility.
##
## If you use this software to prepare a publication, please cite:
##
##     JJ Helmus and SM Collis, JORS 2016, doi: 10.5334/jors.119


In [2]: file = '../../Downloads/ODIM_VOL_HR_NIME_20220816161000.h5'

In [3]: radar = pyart.aux_io.read_odim_h5(file)

In [4]: radar.time
Out[4]: 
{'units': 'seconds since 2022-08-16T16:05:00Z',
 'standard_name': 'time',
 'long_name': 'time_in_seconds_since_volume_start',
 'calendar': 'gregorian',
 'comment': 'Coordinate variable for time. Time at the center of each ray, in fractional seconds since the global variable time_coverage_start',
 'data': array([  1.86549997,   1.91100001,   1.95649981, ..., 244.39399981,
        244.47099996, 244.54849982])}