Fix Date.toString() showing StandardName instead of DaylightName during DST

[Copilot]

Date.prototype.toString() and toTimeString() always used the timezone's StandardName in the parenthetical suffix, even for dates falling within a DST period. For example, a summer date in the Eastern timezone would incorrectly show (Eastern Standard Time) instead of (Eastern Daylight Time).

Changes

• DatePrototype.TimeZoneString(): Check TimeZoneInfo.IsDaylightSavingTime() for the specific timestamp and use DaylightName or StandardName accordingly. Dates outside the DateTimeOffset representable range (year < 0001 or > 9999) fall back to StandardName.

// Before
var tzName = " (" + _timeSystem.DefaultTimeZone.StandardName + ")";

// After
var timeZoneName = timeZone.IsDaylightSavingTime(dateTimeOffset)
    ? timeZone.DaylightName
    : timeZone.StandardName;

• New test ToStringUsesDaylightNameWhenInDst: verifies that a summer date returns the DaylightName and a winter date returns the StandardName.
• Updated 3 existing tests in EngineTests.cs that had incorrect hardcoded expectations — they asserted (Pacific/Eastern Standard Time) for dates that are actually in DST, masking the bug.

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[Copilot]

Pull request overview

Updates Jint’s Date.prototype.toString() / toTimeString() timezone suffix to use the daylight vs. standard timezone name depending on whether the represented instant is in DST, aligning output with typical host behavior and improving correctness for summer dates.

Changes:

• Updated DatePrototype.TimeZoneString to select DaylightName vs StandardName when the date is within the supported DateTimeOffset range.
• Adjusted existing runtime tests to expect DST-aware timezone names (e.g., “Pacific Daylight Time” in June).
• Added a new regression test asserting DST vs standard timezone name selection for an Eastern timezone.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
Jint/Native/Date/DatePrototype.cs	Chooses daylight vs standard timezone name when formatting timezone suffix.
Jint.Tests/Runtime/EngineTests.cs	Updates expected strings to reflect DST-aware timezone naming.
Jint.Tests/Runtime/DateTests.cs	Adds coverage for DST/standard name selection in toString().

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