feat!: Native selector XOR set operation, guarantee consistent selector column-order

[alexander-beedie]

Closes #16822:

• Adds a proper selector xor implementation (inc. .meta, and Python operator integration), with associated docs/tests.

...and some bonus updates/fixes.

• Makes the contains selector signature consistent with the related starts_with and ends_with selectors (eg: can now write the cleaner cs.contains("a","b","c") instead of cs.contains(("a","b","c"))).
• Fixes an issue raised in the Discord with inconsistently ordered selector results - selector set operations should always return matching columns in schema order, irrespective of which selector is on the lhs/rhs of the op.

(The update to contains is breaking if anyone is calling "cs.contains(substring='xyz')" instead of "cs.contains('xyz')". Arguably so is ensuring consistent column return order, though I consider that a fix rather than a breaking change ;)

Example

import polars as pl

df = pl.DataFrame(
    schema={
        "col1": pl.String,
        "col2": pl.Boolean,
        "col3": pl.String,
        "col4": pl.Boolean,
    },
)

df.select(cs.boolean() ^ cs.ends_with("1","2"))
# shape: (0, 2)
# ┌──────┬──────┐
# │ col1 ┆ col4 │
# │ ---  ┆ ---  │
# │ str  ┆ bool │
# ╞══════╪══════╡
# └──────┴──────┘

[codecov]

Codecov Report

Attention: Patch coverage is 89.61039% with 8 lines in your changes missing coverage. Please review.

Project coverage is 81.36%. Comparing base (d9fe109) to head (675cca5).
Report is 1 commits behind head on main.

Files	Patch %	Lines
py-polars/polars/selectors.py	61.53%	4 Missing and 1 partial ⚠️
crates/polars-plan/src/dsl/meta.rs	83.33%	2 Missing ⚠️
...plan/src/logical_plan/conversion/expr_expansion.rs	96.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16833      +/-   ##
==========================================
- Coverage   81.38%   81.36%   -0.02%     
==========================================
  Files        1425     1425              
  Lines      187612   187652      +40     
  Branches     2697     2700       +3     
==========================================
+ Hits       152680   152686       +6     
- Misses      34437    34470      +33     
- Partials      495      496       +1     

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