XS⚠️ ◾ Exclude internal hours from billed days

[AttackOnMorty]

1. What triggered this change? (PBI link, Email Subject, conversation + reason, etc)

As per my conversation with @jimmidier, billed days should not include internal hours because we only care about client hours.

2. What was changed?

This pull request updates the employee billing logic to improve accuracy when calculating billed days, especially regarding project-specific billing and excluding internal projects. The changes primarily refactor how billed days are calculated and used throughout the codebase.

Billing logic improvements

• Replaced usage of GetTotalBilledDays with GetBilledDays in GetFreeEmployeesAction.cs, now calculating billed days for a specific employee and their first project, rather than aggregating across all projects.
• Updated the GetBillableEmployees method to use the new GetBilledDays signature, which takes both the employee and the project, ensuring more precise billing per project.
• Added a new version of GetBilledDays in EmployeesHelper.cs that calculates billed days only for non-SSW (external) projects and ignores internal projects, improving accuracy. The previous methods for total billed days and simple billed days by hours are now commented out.

3. Did you do pair or mob programming?

No

[github-actions]

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Product Code	32
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Subtotal	32
Ignored Code	-
Total	32

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