Add square root calculation functionality

[Copilot]

This PR adds a new feature to calculate the square root of a number, as requested in the issue. The implementation includes:

1. Added a new CalculateSquareRoot method in the DoMath class that:

   • Prompts the user to enter a number
   • Validates the input to ensure it's a valid positive number
   • Calculates the square root using Math.Sqrt() method
   • Displays the result and waits for user input before returning to the menu

2. Updated the main menu to include a new option "7) Calculate square root"

3. Updated the switch statement in the MainMenu method to handle the new option

4. Added a .gitignore file to exclude build artifacts from future commits

How to test

1. Run the application
2. Select option 7 from the main menu
3. Enter a positive number
4. Verify the square root is calculated and displayed correctly

Fixes #2.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• crl3.digicert.com
  • Triggering command: dotnet build (dns block)
• crl4.digicert.com
  • Triggering command: dotnet build (dns block)
• ocsp.digicert.com
  • Triggering command: dotnet build (dns block)
• s.symcb.com
  • Triggering command: dotnet build (dns block)
• s.symcd.com
  • Triggering command: dotnet build (dns block)
• ts-crl.ws.symantec.com
  • Triggering command: dotnet build (dns block)
• ts-ocsp.ws.symantec.com
  • Triggering command: dotnet build (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

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