remove start-end datetime mixin

[dfulu]

Pull Request

Description

Remove the start/end time mixin as it is generally unused. The preferred way to limit the time range of samples is something like this

Note:

Initial discussions around this were that this might be less memory efficient, and that we'd be keeping unused data around by not filtering. However, based on this stack overflow question, I'm not sure we were even freeing up memory with the slicing we were using previously

Checklist:

• [x] My code follows OCF's coding style guidelines
• [x] I have performed a self-review of my own code
• [x] I have made corresponding changes to the documentation
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have checked my code and corrected any misspellings

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (287be67) 78.22% compared to head (9ccd8c9) 78.20%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #264 +/- ## ========================================== - Coverage 78.22% 78.20% -0.03% ========================================== Files 121 121 Lines 5571 5551 -20 ========================================== - Hits 4358 4341 -17 + Misses 1213 1210 -3 ```

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