Update US equity market hours through 2028

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Description

Adds the NYSE holiday and early-close schedule for 2028 to the default US equity market-hours entry.

• Adds the nine NYSE holidays observed in 2028. New Year's Day is intentionally not added because January 1 falls on a Saturday and is not observed by NYSE.
• Adds 1:00 p.m. early closes for July 3 and November 24.
• Adds a focused regression test covering all new dates and the New Year's Day exception.

Source: https://www.nyse.com/trade/hours-calendars

Related Issue

Fixes #9406

Motivation and Context

Without these dates, LEAN can treat 2028 US equity holidays and shortened sessions as regular trading days.

Requires Documentation Change

No.

How Has This Been Tested?

• Parsed Data/market-hours/market-hours-database.json and verified all nine holidays, the New Year's Day exception, and both 1:00 p.m. early closes.
• Ran git diff --check.
• Added CorrectlyReadsUsEquity2028SpecialHours. It was not executed locally because this Windows environment does not have a .NET SDK installed; CI should run it.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Refactor (non-breaking change which improves implementation)
• Performance (non-breaking change which improves performance. Please add associated performance test and results)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Non-functional change (xml comments/documentation/etc)

Checklist:

• My code follows the code style of this project.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed. The test could not be run locally because no .NET SDK is installed.
• My branch follows the naming convention bug-<issue#>-<description> or feature-<issue#>-<description>.