v2.1.0

• Introduces LocalDate (+ InvalidLocalDate) and documentation/tests for date-only operations and projecting an Instant into a civil date.
• Adds Precision and extends Instant::toIso8601() to optionally emit milliseconds/microseconds; updates offset datetime decoding to accept fractional seconds.
• Refactors multiple unit tests toward more explicit Given/When/Then steps and expands Instant coverage for precision formatting.