Python Polars 0.18.4

🚀 Performance improvements

• don't initialize memory before row-encoding (#9435)
• further optimize datetime conversion (#9452)
• speedup datetime conversion (#9432)
• reduce page faults in q1 ~-30% (#9423)
• reduce rayon/idle time in streaming (#9416)

✨ Enhancements

• add drop_first parameter for to_dummies (issue #8246) (#9143)
• raise if window size in rolling functions isn't strictly positive (#9465)
• serializable python functions in expressions (#9462)
• add infer schema len to json_extract (#9478)
• Adds (Most) Remaining Trig Functions to SQLContext (#9453)
• update error handling msg for sql functions (#9474)
• Update LazyFrame.__repr__ (#9460)
• support inversion of first & last selectors, additional minor repr improvements (#9456)
• add str.titlecase (#9457)
• raise if period is negative in groupby_rolling (#9445)
• enhanced polars.selectors repr and implicit application of as_expr when broadcasting (#9450)
• add SQL round support (#9330)
• dont error for time-zone-aware parsing if time zone is UTC (#9414)

🐞 Bug fixes

• ensure that trying to use a string as a dtype raises a consistent error on both DataFrame and Series init (#9493)
• fix race condition in out-of-core sort (#9521)
• unset sortedness for local date and local datetime (#9515)
• maintain sortedness flags on append/extend (#9496)
• fix serde for small integer dtypes (#9495)
• raise if window size in rolling functions isn't strictly positive (#9465)
• Fix empty list or Series selections on DF or Series (#8660)
• groupby rolling with negative offset (#9428)
• pl.lit with datetime was producing slightly incorrect results (#9438)
• read_csv was parsing dates incorrectly when the dtype was overridden (#9420)
• Compute Spearman rank correlations using average ra… (#9415)
• Fix rolling min/max when window is empty (#9406)

🛠️ Other improvements

• don't pickle pyarrow dataset (#9523)
• fix rendering of examples (#9482)
• Warn for future change of closed default value in rolling functions (#9470)
• Document aggregate_function=None in pivot (#9473)
• Docstrings for expressions and dtypes (#9351)
• fix typo in rolling_* docstrings (#9449)
• Deprecate some expr input parsing behavior (#9455)
• improve date-range docs (#9451)
• Improve docstrings rolling functions (#9215)
• Remove _tempdir module references (#9427)
• fix typo in Series.qcut (#9421)
• Add some documentation on the CI workflows (#9404)

Thank you to all our contributors for making this release possible!
@EdmundsEcho, @MarcoGorelli, @SeanTroyUWO, @alexander-beedie, @baggiponte, @braaannigan, @datapythonista, @magarick, @mcrumiller, @messense, @mgperry, @mishpat, @ritchie46, @stinodego, @tarrafil, @universalmind303 and @zundertj