feat: Improved time-string parsing and inference (generally, and via the SQL interface)

[alexander-beedie]

Addresses an Issue raised on the Discord (in the #sql channel) by @etrotta.

• Generic time-string parsing improvement (adds %R chrono hour-minute format to the set of recognised time specifiers - which we already identify in datetime strings).
• Brings SQL temporal literal string inference in-line with the underlying to_datetime and to_time functions so that hour-minute format (%R, aka:%H:%M) is also recognised in the SQL interface (both standalone, as a time, and as part of a larger datetime/timestamp string). A subsequent/follow-up PR will bring a similar improvement to SQL CAST ops.

Example

Use of '%H:%M' literal strings in WHERE clauses:

import polars as pl

df = pl.DataFrame({
    "tm": [time(0,45,10), time(10,30,59), time(18,5,20), time(12,25,5)],
    "val": ["aaa", "bbb", "ccc" ,"ddd"],
})
df.sql("SELECT * FROM self WHERE tm > '12:00' ORDER BY tm")
# shape: (2, 2)
# ┌──────────┬─────┐
# │ tm       ┆ val │
# │ ---      ┆ --- │
# │ time     ┆ str │
# ╞══════════╪═════╡
# │ 12:25:05 ┆ ddd │
# │ 18:05:20 ┆ ccc │
# └──────────┴─────┘

Properly inferred by str.to_time():

pl.DataFrame({
    "tmstr": ["00:01", "23:00", "14:30"],
}).with_columns(
    tm = pl.col("tmstr").str.to_time(),
)
# shape: (3, 2)
# ┌───────┬──────────┐
# │ tmstr ┆ tm       │
# │ ---   ┆ ---      │
# │ str   ┆ time     │
# ╞═══════╪══════════╡
# │ 00:01 ┆ 00:01:00 │
# │ 23:00 ┆ 23:00:00 │
# │ 14:30 ┆ 14:30:00 │
# └───────┴──────────┘

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.89%. Comparing base (0d5fdef) to head (ba6b5f3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #22606      +/-   ##
==========================================
- Coverage   80.90%   80.89%   -0.02%     
==========================================
  Files        1656     1656              
  Lines      234036   234036              
  Branches     2752     2752              
==========================================
- Hits       189349   189323      -26     
- Misses      44027    44053      +26     
  Partials      660      660              

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