Linear regression: Refactor unit tests

[luccalb]

User Story

1. As a RTDIP developer
2. I want to make sure that my unit tests cover enough edge cases
3. So that i can ensure a high quality and good usability

Additional context

Related to #60

Acceptance Criteria

• Make sure the unit tests include example data provided by shell
• Tests should handle invalid data types
• At least one test should be a load test, where minium 1000 datapoints are processed, without the component crashing/freezing
• It's ensured that data types are validated and descriptive error is thrown in case of violation or if conversion is not possible

Definition of Done

• Test cases have been created and are running successfully
• Documentation for any new component was added
• Github Actions are running without errors