feat: add EventDataFrame.add_trial_column()

[dkrako]

Description

A helpful method for working on #655 In hindsight I'm not so sure anymre if it is useful at all to have it as an EventDataFrame method

Implemented changes

• [x] implement add_trial_column() method

Type of change

• [x] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• [x] single column
• [x] two columns
• [x] test for exception raising

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 (c9ff834) 100.00% compared to head (645c10f) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #671 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 54 54 Lines 2386 2396 +10 Branches 597 601 +4 ========================================= + Hits 2386 2396 +10 ```

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