Release v0.0.2

[rhannequin]

0.0.2 - 2026-07-14

The first functional release. It ships the numeric core and the two value
objects the rest of the library is built on: Instant and Duration. The
scale conversions are not here yet, so an instant is built directly from a
TAI Julian Date for now.

Features

• Add Numeric::TwoPartFloat, a number kept as a high and a low Float for
  about twice the precision of one, with Shewchuk error-free arithmetic
• Add Numeric::Exact, a value kept as an exact Rational, with no rounding
• Add the precision contract: every value carries a precision, :standard or
  :exact, set when it is built and never changed. Mixing the two promotes
  the result to :exact instead of dropping to :standard
• Add Horologium.configure for the set-once default precision, and
  Horologium.with_precision for a scoped, per-fiber override
• Add Instant, a frozen point on the TAI timeline, built with
  Instant.from_tai_julian_date
• Add Duration, a frozen span in SI seconds, built with Duration.seconds,
  Duration.days, and Duration.nanoseconds
• Add instant and duration arithmetic: shift an instant by a duration, and
  subtract two instants to measure the duration between them
• Add Instant#equal_within? for comparison inside a tolerance
• Guard against meaningless operations: adding two instants raises
  DimensionalError

Full Changelog: v0.0.1...v0.0.2