fix: don't fail in event fill if event onsets/offsets not within timesteps

[dkrako]

Description

The fill method raised an exception if there were events with onsets/offsets outside the timestep space passed via time.

Implemented changes

• [x] handle events with onset after last timestep (ignore and continue)
• [x] handle events with onset before first timestep (use first timestep as start)
• [x] handle events with offset before first timestep (ignore and continue)
• [x] handle events with onset before last timestep (use last timestep as end)

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• [x] added several tests with events exceeding timestep boundaries

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules
• [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 (5b90d55) 100.00% compared to head (f54a1ac) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #656 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 54 54 Lines 2366 2374 +8 Branches 590 594 +4 ========================================= + Hits 2366 2374 +8 ```

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