feat: Added possibility to use datetime nanoseconds precision by pandas.Timestamp

[bednar]

Closes #124

Proposed Changes

The Python's datetime doesn't support precision with nanoseconds so the library during writes and queries ignores everything after microseconds.

If you would like to use datetime with nanosecond precision you should use pandas.Timestamp that is replacement for python datetime.datetime object and also you should set a proper DateTimeHelper to the client.

from influxdb_client import Point, InfluxDBClient
from influxdb_client.client.util.date_utils_pandas import PandasDateTimeHelper
from influxdb_client.client.write_api import SYNCHRONOUS

"""
Set PandasDate helper which supports nanoseconds.
"""
import influxdb_client.client.util.date_utils as date_utils

date_utils.date_helper = PandasDateTimeHelper()

...

https://github.com/influxdata/influxdb-client-python/blob/feat/nanoseconds/examples/nanosecond_precision.py

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• pytest tests completes successfully
• Commit messages are in semantic format
• Sign CLA (if not already signed)

[codecov-commenter]

Codecov Report

Merging #141 into master will increase coverage by 0.01%.
The diff coverage is 96.87%.

@@            Coverage Diff             @@
##           master     #141      +/-   ##
==========================================
+ Coverage   88.93%   88.94%   +0.01%     
==========================================
  Files          23       24       +1     
  Lines        1870     1882      +12     
==========================================
+ Hits         1663     1674      +11     
- Misses        207      208       +1     

Impacted Files	Coverage Δ
influxdb_client/client/util/date_utils.py	94.73% <94.73%> (ø)
influxdb_client/client/flux_csv_parser.py	91.71% <100.00%> (ø)
influxdb_client/client/util/date_utils_pandas.py	100.00% <100.00%> (ø)
influxdb_client/client/write/point.py	98.36% <100.00%> (-0.06%)	⬇️

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