Min/Max Date Fix

[jbouder]

Description

• Ensure date picker can handle timestamp numbers as min/max.
• Added unit tests

Related Issue

Resolves #468

Motivation and Context

• Bug Fix

How Has This Been Tested?

• Local Testing

Screenshots (if appropriate):

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.59%. Comparing base (e327e93) to head (f70957a).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #469   +/-   ##
=======================================
  Coverage   99.59%   99.59%           
=======================================
  Files          51       51           
  Lines         997      997           
  Branches      346      346           
=======================================
  Hits          993      993           
  Misses          4        4           

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[Copilot]

Pull request overview

This PR fixes a bug (issue #468) where the DatePicker component crashes with "p.toISOString is not a function" when minDate, maxDate, or dateRange is passed as a string (e.g., from Storybook controls). The root cause was that the internal getDateString helper only accepted string | Date, but when a string was coerced to a number by some callers (or a numeric timestamp was passed directly), it had no handling for the number type.

Changes:

• Extended the minDate, maxDate, and dateRange prop types to accept number (Unix timestamp in ms) in addition to Date | string.
• Updated getDateString to handle the number type by wrapping it in new Date() before formatting, and added a JSDoc comment.
• Added unit tests for all three props with numeric timestamp inputs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
packages/comet-uswds/src/components/date-picker/date-picker.tsx	Adds number to prop types for minDate, maxDate, dateRange; updates getDateString to accept/handle numbers; adds JSDoc.
packages/comet-uswds/src/components/date-picker/date-picker.test.tsx	Adds three new tests covering minDate, maxDate, and dateRange with numeric timestamp inputs.

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