Add unit tests for observatory module

Description

All functions are tested, and a testing file with meteorological data has been added to the repository.

Related Issue

Closes #99 (closed), related to #98 (closed)

How Has This Been Tested?

manually run tests with pytest

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.