Enum literals evaluate to equal for CSE when one dtype is subset of another

[mcrumiller]

Checks

• [X] I have checked that this issue has not already been reported.
• [X] I have confirmed this bug exists on the latest version of Polars.

Issue description

If two enums are used in a collect with CSE enabled, then their literals will evaluate to true, even if they have different categories, as long as one's categories is a subset of the other's.

import polars as pl

dt1 = pl.Enum(["a"])         # CAUSES ERROR
# dt1 = pl.Enum(["a", "c"])  # DOES NOT CAUSE ERROR -- dt1 is not a subset of dt2
dt2 = pl.Enum(["a", "b"])

out = pl.LazyFrame().select(
    pl.lit("a", dtype=dt1).alias("dt1"),
    pl.lit("a", dtype=dt2).alias("dt2"),
).collect()

print(out.dtypes)

Second literal should have categories=['a', 'b'].

[Enum(categories=['a']), Enum(categories=['a'])]

Installed versions

main

[mcrumiller]

@c-peters

[c-peters]

There seems to be bug related to equality check for the underlying categories. It is not exhaustive at the moment