[InfluxDB] Improve export adapter interfaces, and naming things

[amotl]

Pulled out of GH-148, this patch sets the stage for more easily bringing in different database adapters when exporting data.

Other than this, there are also a few maintenance adjustments.

[codecov]

Codecov Report

Patch coverage: 77.06% and project coverage change: +10.83 🎉

Comparison is base (b2817b6) 67.43% compared to head (52e8d5e) 78.26%.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #151       +/-   ##
===========================================
+ Coverage   67.43%   78.26%   +10.83%     
===========================================
  Files          65       55       -10     
  Lines        3565     3009      -556     
===========================================
- Hits         2404     2355       -49     
+ Misses       1161      654      -507     

Flag	Coverage Δ
unittests	78.26% <77.06%> (+10.83%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
kotori/io/protocol/util.py	62.11% <45.94%> (-4.83%)	⬇️
kotori/io/export/database.py	86.48% <86.48%> (ø)
kotori/daq/storage/influx.py	78.37% <100.00%> (+19.28%)	⬆️
kotori/io/protocol/forwarder.py	96.38% <100.00%> (ø)
kotori/io/protocol/http.py	83.45% <100.00%> (+0.69%)	⬆️
kotori/io/protocol/influx.py	93.75% <100.00%> (+32.63%)	⬆️
kotori/io/protocol/target.py	60.91% <100.00%> (ø)

... and 10 files with indirect coverage changes

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