chore: migrate deprecated polars funtions

[josephine-funken]

Description

The use of deprecated pandas functions groupby, lengths and map were refactored. The respective DeprecationWarnings no longer occur.

Fixes issue #611

Implemented changes

• [x] Migrate groupby to group_by
• [x] Migrate lengths to len
• [x] Migrate map to map_batches
• [x] Remove ignores from pyproject.toml

Type of change

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

How Has This Been Tested?

Changes have not been tested because they do not change the functionality.

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [ ] 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
• [ ] 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 lines are covered by tests :white_check_mark:

Comparison is base (b6538a3) 100.00% compared to head (5a5d2e6) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #612 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 52 52 Lines 2348 2348 Branches 587 587 ========================================= Hits 2348 2348 ``` | [Files](https://app.codecov.io/gh/aeye-lab/pymovements/pull/612?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/events/processing.py](https://app.codecov.io/gh/aeye-lab/pymovements/pull/612?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aeye-lab#diff-c3JjL3B5bW92ZW1lbnRzL2V2ZW50cy9wcm9jZXNzaW5nLnB5) | `100.00% <ø> (ø)` | | | [src/pymovements/gaze/gaze\_dataframe.py](https://app.codecov.io/gh/aeye-lab/pymovements/pull/612?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)` | | | [src/pymovements/gaze/transforms.py](https://app.codecov.io/gh/aeye-lab/pymovements/pull/612?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aeye-lab#diff-c3JjL3B5bW92ZW1lbnRzL2dhemUvdHJhbnNmb3Jtcy5weQ==) | `100.00% <ø> (ø)` | |

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