feat: Add an is_literal method to expression meta namespace

[alexander-beedie]

Added a simple is_literal extension to the "meta" namespace.

(There's a slight subtlety when matching datetime literals, as an implicit strict-cast gets injected; otherwise it's just simple matching).

Examples

from datetime import datetime
import polars as pl

for value in (123, "four five", datetime.now()):
    e = pl.lit(value)
    e.meta.is_literal()
    # True
    
    e = pl.lit(value).alias("foo")
    e.meta.is_literal()
    # False
    
    e = pl.lit(value).alias("foo")
    e.meta.is_literal(allow_aliasing=True)
    # True

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.56%. Comparing base (8cb7839) to head (e4246d3).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #19773   +/-   ##
=======================================
  Coverage   79.55%   79.56%           
=======================================
  Files        1544     1544           
  Lines      213240   213253   +13     
  Branches     2441     2441           
=======================================
+ Hits       169643   169665   +22     
+ Misses      43048    43039    -9     
  Partials      549      549           

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[etiennebacher]

This should be listed in meta.rst as well? (Just noticing because of #19744)

[alexander-beedie]

This should be listed in meta.rst as well? (Just noticing because of #19744)

It certainly should - thx for the reminder (fixed) 😉