$3.$Case study: Suppose you are tasked with designing a C# program to manage company employees. The requirements include defining different types of employees, such as full$-$time, part$-$time, and contractual, each with specific attributes and behaviors. Implement the necessary structures, interfaces, abstract classes, and inheritance to fulfill these requirements.

$3\mathrm{.}1$ a$).$ Define a structure named $$Address$$ with the following fields:

$$ string Street

$$ string City

$$ string State

$$ int ZipCode

b$).$ Define an interface named IEmployee with the following methods:

$-$ void DisplayDetails$()$: This method should display the employee's details.

$-$ double CalculateSalary$()$: This method should calculate and return the employee's salary.

c$).$ Define an abstract class named Employee that implements the IEmployee interface and has the following properties and methods:

$-$ Properties:

$$ int EmployeeId

$$ string FullName

$$ Address EmployeeAddress

$-$ Methods:

$$ abstract double CalculateSalary$()$: This method should be implemented by derived classes to calculate the salary of specific types of employees.

$$ Virtual void DisplayDetails$()$: This method should display the employee's details.