Add Duration, a nanosecond-resolution timedelta

[jaraco]

What

Adds tempora.Duration: a Decimal-backed span of time with nanosecond resolution, for expressing and comparing intervals too short for datetime.timedelta (which bottoms out at one microsecond).

>>> print(tempora.Duration.parse('34.2 nsec'))
34.2 nsec
>>> print(tempora.Duration(microseconds=1.6))
1.6 µsec
>>> tempora.Duration.parse('38.1 nsec') / tempora.Duration.parse('34.2 nsec')
Decimal('1.114035087719298245614035088')

It constructs from nanoseconds or keyword units, parses textual durations (via parse_nanoseconds), and renders itself in the most natural unit (nsec/µsec/msec/sec) using a RangeMap. It supports the arithmetic these comparisons need — including division of one Duration by another to yield a dimensionless ratio, which datetime.timedelta offers but attotime does not — plus scaling, ordering, bool, and interconversion with datetime.timedelta.

Motivation

For jaraco/pytest-perf#18. pytest-perf compares timeit results; sub-microsecond timings (e.g. python/importlib_metadata#533) rounded to timedelta(0), collapsing its variance calculation. parse_nanoseconds (5.11) exposed a bare Decimal, but a scalar with implied units is a poor substitute for a value carrying its own magnitude and units — hence this richer type.

attotime was considered and set aside: attotimedelta / attotimedelta is unsupported, and it's an extra dependency; a bespoke type keeps the ratio ergonomic and the __str__ unit-aware.

Doctested; coh test green.

🤖 Generated with Claude Code