Enable floordiv on durations: duration // duration

[rhshadrach-8451]

Description

Python allows

import datetime as dt

print(dt.timedelta(hours=1, minutes=30) // dt.timedelta(minutes=35))
# 2

This seems to me to be well-defined and useful. Polars gives

df = pl.DataFrame({"a": dt.timedelta(hours=1, minutes=30)})
df.with_columns(b=pl.col("a") // pl.duration(minutes=35))
# InvalidOperationError: floor_div not allowed on duration[μs] and duration[μs]

#12330 has a list of allowed arithmetic operations in the OP and duration // duration is not mentioned there, but it is also not discussed in that issue. cc @Wainberg

Somewhat similar issues (but also don't discuss duration // duration):

• Duration Arithmetic #9637
• Can't multiply or divide a Duration Series by an integer #14094