Allow Series.pow/2 to receive float series on both sides and negative base

[Jhonatannunessilva]

This PR allows the Series.pow/2 function to receive float series on both sides and a negative base.

This is part of #512

Before this PR:

iex(1)> s1 = Explorer.Series.from_list([1.0, 2.5, :nan, :infinity, :neg_infinity])
#Explorer.Series<
  Polars[5]
  float [1.0, 2.5, NaN, Inf, -Inf]
>

iex(2)> s2 = Explorer.Series.from_list([1.0, 3.5, :nan, :infinity, :neg_infinity])
#Explorer.Series<
  Polars[5]
  float [1.0, 3.5, NaN, Inf, -Inf]
>

iex(3)> Explorer.Series.pow(s1, s2)                                               
** (RuntimeError) Data types don't match: Series of dtype: Float64 != Int64
    (explorer 0.6.0-dev) lib/explorer/polars_backend/shared.ex:26: Explorer.PolarsBackend.Shared.apply_series/3

iex(3)> s3 = Explorer.Series.from_list([1, 2, 3])                                 
#Explorer.Series<
  Polars[3]
  integer [1, 2, 3]
>

iex(4)> Explorer.Series.pow(-2, s3)                                               
thread '<unnamed>' panicked at 'called `Result::unwrap()` on an `Err` value: {error, badarg}', src/series.rs:829:54
                                                                                                                   note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
                                        ** (ErlangError) Erlang error: :nif_panicked
    (explorer 0.6.0-dev) Explorer.PolarsBackend.Native.s_pow_f_lhs(#Explorer.PolarsBackend.Series<
  shape: (3,)
  Series: '' [i64]
  [
        1
        2
        3
  ]
>, -2)
    (explorer 0.6.0-dev) lib/explorer/polars_backend/shared.ex:23: Explorer.PolarsBackend.Shared.apply_series/3

After this PR:

iex(1)> s1 = Explorer.Series.from_list([1.0, 2.5, :nan, :infinity, :neg_infinity])
#Explorer.Series<
  Polars[5]
  float [1.0, 2.5, NaN, Inf, -Inf]
>

iex(2)> s2 = Explorer.Series.from_list([1.0, 3.5, :nan, :infinity, :neg_infinity])      
#Explorer.Series<
  Polars[5]
  float [1.0, 3.5, NaN, Inf, -Inf]
>

iex(3)> Explorer.Series.pow(s1, s2)
#Explorer.Series<
  Polars[5]
  float [1.0, 24.705294220065465, NaN, Inf, 0.0]
>

iex(4)> s3 = Explorer.Series.from_list([1, 2, 3])
#Explorer.Series<
  Polars[3]
  integer [1, 2, 3]
>

iex(5)> Explorer.Series.pow(-2, s3)
#Explorer.Series<
  Polars[3]
  integer [-2, 4, -8]
>

[philss]

Thanks for improving the test suite! ❤️

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