Fix PM-settled index options settlement time on 3rd Friday

[JosueNina]

Description

GetSettlementDateTime was applying AM settlement to PM-settled tickers (SPXW, RUTW, etc.) on the 3rd Friday because IsStandard() only checked the date, not the ticker. This made timeTillExpiry negative, zeroing out IV and all Greeks for the rest of the session.
Added IndexOptionSymbol.IsAMSettled() to guard the AM settlement path, and a test that confirms IV and Delta are non-zero for a PM-settled contract on expiration day.

Related Issue

Closes #9346

Motivation and Context

N/A

Requires Documentation Change

N/A

How Has This Been Tested?

It was tested using unit tests.

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.
• My branch follows the naming convention bug-<issue#>-<description> or feature-<issue#>-<description>