Convert reliability calibration tests pytest

[lucyleeow]

Advantages of using pytest

• prevents code duplication, e.g., with use of parametrize. This is especially useful to test enhancements (grid and site, point by point and aggregate)
• fixtures allow standardisation across test scripts of sample input cubes and enables set up code to be in one place, separate from test code

This work has already started here: lucyleeow#1
This issue relates to conversion of the remaining reliability calibration tests to pytest.
Note there has already been some discussion via other channels about this.

cc @tjtg

[tjtg]

This has been mostly addressed in #1667 and #1687 - these two PRs cover AggregateReliabilityCalibrationTables, ConstructReliabilityCalibrationTables and ManipulateReliabilityTable.

ApplyReliabilityCalibration is still remaining with UnitTest style tests.