Add dateTime range tests.

[davidlehn]

• Work in progress.
• Pre-epoch dates are failing to roundtrip. Looks like they fail in slightly different ways depending on the date. Might get back 0 or internal cbor errors.
• dateTime codec needs fixing, should add tests and check date codec too.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.96%. Comparing base (349f9b7) to head (4978120).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #109      +/-   ##
==========================================
+ Coverage   92.17%   92.96%   +0.79%     
==========================================
  Files          35       35              
  Lines        2682     2685       +3     
==========================================
+ Hits         2472     2496      +24     
+ Misses        210      189      -21     

Files with missing lines	Coverage Δ
lib/codecs/ValueEncoder.js	95.45% <100.00%> (+0.05%)	⬆️
lib/codecs/XsdDateEncoder.js	85.00% <100.00%> (+8.07%)	⬆️
lib/codecs/XsdDateTimeEncoder.js	89.83% <100.00%> (+26.03%)	⬆️

... and 1 file with indirect coverage changes

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[dlongley]

This PR is ready for review now.