feat: Allow parsing of compact ISO 8601 strings

[orlp]

This allows Polars to parse compact ISO 8601 datetime strings which lack any separators such as 20190418T224555.555123Z which are commonly found in logfiles/filenames.

I also drastically reduced the number of patterns by using chrono's %.f instead of repeating the pattern for %.3f, %.6f, etc.

@MarcoGorelli

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.83%. Comparing base (59f1ee9) to head (3916fd3).
⚠️ Report is 19 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #24629   +/-   ##
=======================================
  Coverage   81.83%   81.83%           
=======================================
  Files        1689     1688    -1     
  Lines      230063   229981   -82     
  Branches     2974     2974           
=======================================
- Hits       188262   188198   -64     
+ Misses      41048    41030   -18     
  Partials      753      753           

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[MarcoGorelli]

This allows Polars to parse compact ISO 8601 datetime strings which lack any separators

nice!

I also drastically reduced the number of patterns by using chrono's %.f

🤔 I recalled there being some issue with this due to the length of the string non being inferrable from the format, but perhaps that's not an issue anymore, or it doesn't affect the path where the format is auto-inferred by Polars anyway, as it looks like it doesn't go to

polars/crates/polars-time/src/chunkedarray/string/strptime.rs

Line 303 in 37e4452

pub(super) fn fmt_len(fmt: &[u8]) -> Option<u16> {

at all in this case anyway

Should be fine then!

[Julian-J-S]

I also drastically reduced the number of patterns by using chrono's %.f instead of repeating the pattern for %.3f, %.6f, etc.

Very vaguely remember that the fixed size versions had performance improvements and some other benefits I don't quite remember. But could be solved by now 🤓