feat: Add SQL support for the DELETE statement

[alexander-beedie]

Adds SQL support for the DELETE FROM <table> [WHERE <constraint>] statement.
(Validated edge cases -such as constraints involving null values- against SQLite).

Example

import polars as pl

df = pl.DataFrame({
    "id": [100, 200, 300],
    "dt": [date(2020, 10, 10), date(1999, 1, 2), date(2001, 7, 5)],
    "v1": [3.5, -4.0, None],
    "v2": [10.0, 2.5, -1.5],
})
# ┌─────┬────────────┬──────┬──────┐
# │ id  ┆ dt         ┆ v1   ┆ v2   │
# │ --- ┆ ---        ┆ ---  ┆ ---  │
# │ i64 ┆ date       ┆ f64  ┆ f64  │
# ╞═════╪════════════╪══════╪══════╡
# │ 100 ┆ 2020-10-10 ┆ 3.5  ┆ 10.0 │
# │ 200 ┆ 1999-01-02 ┆ -4.0 ┆ 2.5  │
# │ 300 ┆ 2001-07-05 ┆ null ┆ -1.5 │
# └─────┴────────────┴──────┴──────┘

df.sql("DELETE FROM self WHERE v1 < 0")
# ┌─────┬────────────┬──────┬──────┐
# │ id  ┆ dt         ┆ v1   ┆ v2   │
# │ --- ┆ ---        ┆ ---  ┆ ---  │
# │ i64 ┆ date       ┆ f64  ┆ f64  │
# ╞═════╪════════════╪══════╪══════╡
# │ 100 ┆ 2020-10-10 ┆ 3.5  ┆ 10.0 │
# │ 300 ┆ 2001-07-05 ┆ null ┆ -1.5 │
# └─────┴────────────┴──────┴──────┘

df.sql("DELETE FROM self WHERE EXTRACT(year FROM dt) >= 2000")
# ┌─────┬────────────┬──────┬─────┐
# │ id  ┆ dt         ┆ v1   ┆ v2  │
# │ --- ┆ ---        ┆ ---  ┆ --- │
# │ i64 ┆ date       ┆ f64  ┆ f64 │
# ╞═════╪════════════╪══════╪═════╡
# │ 200 ┆ 1999-01-02 ┆ -4.0 ┆ 2.5 │
# └─────┴────────────┴──────┴─────┘

[codecov]

Codecov Report

Attention: Patch coverage is 71.42857% with 16 lines in your changes missing coverage. Please review.

Project coverage is 79.88%. Comparing base (c1e493a) to head (3365d20).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-sql/src/context.rs	71.42%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21190      +/-   ##
==========================================
- Coverage   79.88%   79.88%   -0.01%     
==========================================
  Files        1593     1593              
  Lines      227752   227801      +49     
  Branches     2600     2600              
==========================================
+ Hits       181936   181970      +34     
- Misses      45219    45234      +15     
  Partials      597      597              

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