Adding backend testing infrastructure

[aaron-wu1]

adding pytest as testing framework adding pytest-postgresql as a postgres testing fixture refactored backend modules added testing for adding power cell, setting user auth tokens

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 93.75000% with 8 lines in your changes missing coverage. Please review.

Files	Patch %	Lines
backend/tests/conftest.py	86.95%	6 Missing :warning:
backend/api/auth/routes.py	33.33%	2 Missing :warning:

Flag	Coverage Δ
backend	59.30% <93.75%> (?)
frontend	76.00% <ø> (ø)

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Files	Coverage Δ
backend/api/__init__.py	97.22% <100.00%> (ø)
backend/api/auth/auth.py	23.52% <100.00%> (ø)
backend/api/config.py	100.00% <100.00%> (ø)
backend/api/models/__init__.py	100.00% <100.00%> (ø)
backend/api/models/cell.py	80.00% <100.00%> (ø)
backend/api/models/data.py	77.77% <ø> (ø)
backend/api/models/logger.py	90.00% <100.00%> (ø)
backend/api/models/oauth_token.py	88.23% <ø> (ø)
backend/api/models/power_data.py	49.15% <ø> (ø)
backend/api/models/sensor.py	31.08% <ø> (ø)
... and 24 more

... and 5 files with indirect coverage changes