fix(python): silence Series.apply inefficient apply warning when calling Expr.apply

[MarcoGorelli]

The warning's currently being shown twice, once from Expr.apply and once from Series.apply :

In [1]: my_dict = {1: "1", 2: "2", 3: "3"}
   ...: df = pl.DataFrame({"a": [1, 2, 3]})
   ...: df.select(pl.col("a").apply(lambda x: x**2))
   ...: 
<ipython-input-1-2741e0b26152>:3: PolarsInefficientApplyWarning: 
Expr.apply is significantly slower than the native expressions API.
Only use if you absolutely CANNOT implement your logic otherwise.
In this case, you can replace your `apply` with the following:
  -  pl.col("a").apply(lambda x: ...)
  +  pl.col("a") ** 2

  df.select(pl.col("a").apply(lambda x: x**2))
sys:1: PolarsInefficientApplyWarning: 
Series.apply is significantly slower than the native series API.
Only use if you absolutely CANNOT implement your logic otherwise.
In this case, you can replace your `apply` with the following:
  -  s.apply(lambda x: ...)
  +  s ** 2

Out[1]: 
shape: (3, 1)
┌─────┐
│ a   │
│ --- │
│ i64 │
╞═════╡
│ 1   │
│ 4   │
│ 9   │
└─────┘

Adding a test to check the exact warning message so this doesn't happen again