Typo: pandas -> polars (#3434)

## 📝 Summary

Fix typos: `pandas` -> `polars`

## 🔍 Description of Changes

Fix typos where `import polars` is incorrectly written as `import
pandas`

## 📋 Checklist

- [x] I have read the [contributor
guidelines](https://github.com/marimo-team/marimo/blob/main/CONTRIBUTING.md).
- [ ] For large changes, or changes that affect the public API: this
change was discussed or approved through an issue, on
[Discord](https://marimo.io/discord?ref=pr), or the community
[discussions](https://github.com/marimo-team/marimo/discussions) (Please
provide a link if applicable).
- [ ] I have added tests for the changes made.
- [ ] I have run the code and verified that it works as expected.

## 📜 Reviewers

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docs/guides/working_with_data/dataframes.md

@@ -116,7 +116,7 @@ transformed_df.value
 ```python
 # Cell 1
 import marimo as mo
-import pandas as pl
+import polars as pl
 
 df = pl.DataFrame({"person": ["Alice", "Bob", "Charlie"], "age": [20, 30, 40]})
 transformed_df = mo.ui.dataframe(df)
@@ -229,7 +229,7 @@ table.value
 ```python
 # Cell 1 - display a dataframe
 import marimo as mo
-import pandas as pl
+import polars as pl
 
 df = pl.DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
 table = mo.ui.table(df, selection="multi")