Idiomatic polars `peek_dict` method

[alexander-beedie]

Extremely minor tweak for more idiomatic Polars peek_dict. (We have a "named" param on the row^1 method for this).

[goodwanghan]

Welcome @alexander-beedie ! Thanks for making the change.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (cb6733e) 100.00% compared to head (db94458) 100.00%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #453 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 128 128 Lines 12077 12077 ========================================= Hits 12077 12077 ``` | [Impacted Files](https://codecov.io/gh/fugue-project/fugue/pull/453?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fugue-project) | Coverage Δ | | |---|---|---| | [fugue\_polars/polars\_dataframe.py](https://codecov.io/gh/fugue-project/fugue/pull/453?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fugue-project#diff-ZnVndWVfcG9sYXJzL3BvbGFyc19kYXRhZnJhbWUucHk=) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fugue-project). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fugue-project)

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