Invalid dtypes should raise an error

[kevinheavey]

Polars version checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of Polars.

Issue description

If you pass something that's not a dtype to pl.Series, it won't complain and will instead just ignore the dtype argument. This is probably not what we want, especially when people coming from pandas might try to do things like dtype="uint32".

The following example prints out:

shape: (2,)
Series: '' [i64]
[
        1
        2
]

Reproducible example

import polars as pl
print(pl.Series([1, 2], dtype="mayonnaise"))

Expected behavior

Raise an error.

Installed versions

---Version info---
Polars: 0.15.8
Index type: UInt32
Platform: Linux-5.15.85-1-MANJARO-x86_64-with-glibc2.36
Python: 3.11.0 | packaged by conda-forge | (main, Oct 25 2022, 06:24:40) [GCC 10.4.0]
---Optional dependencies---
pyarrow: 10.0.1
pandas: 1.5.2
numpy: 1.23.5
fsspec: 2022.11.0
connectorx: <not installed>
xlsx2csv: <not installed>
matplotlib: 3.6.2