Update GazeDataFrame Docstring to Include Missing trial_columns Argument

[jakobchwastek]

I noticed the trial_columns argument was missing from the docstring of GazeDataFrame's constructor. Added it to clarify the usage and effect of this argument.

Changes

• Updated the GazeDataFrame constructor docstring to include a explanation for the trial_columns parameter.

Type of Change

• [x] Docs update

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (47e29b7) 100.00% compared to head (9ce1717) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #494 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 48 48 Lines 2081 2081 Branches 505 505 ========================================= Hits 2081 2081 ``` | [Files Changed](https://app.codecov.io/gh/aeye-lab/pymovements/pull/494?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aeye-lab) | Coverage Δ | | |---|---|---| | [src/pymovements/gaze/gaze\_dataframe.py](https://app.codecov.io/gh/aeye-lab/pymovements/pull/494?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aeye-lab#diff-c3JjL3B5bW92ZW1lbnRzL2dhemUvZ2F6ZV9kYXRhZnJhbWUucHk=) | `100.00% <ø> (ø)` | |

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