Updates to address changes in pandas plus testing updates

[kaklise]

This PR includes the following:

• Updated code to address changes in Pandas, including deprecation of is_monotonic and append. These updates address issues check_timestamp failed due to deprecation of 'is_monotonic' #76 and Pandas 2.0: Dataframe.append() deprecated #75. Other changes include updates to the use of groupby and read_csv
• Updated tests to use pytest instead of nose
• Added Python 3.10 to testing suite. Dropped Python 3.6 and 3.7

[coveralls]

coverage: 85.43% (+0.2%) from 85.265% when pulling 9979ba4 on kaklise:update into 3f62dd2 on sandialabs:main.