Update instructions to require automatically building and formatting

[westey-m]

Motivation and Context

Copilot is often creating code that fails to build and has formatting errors, so adding some instructions to build and format after any changes.

Description

• Update instructions to require automatically building and formatting

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull request overview

This PR updates the GitHub Copilot instructions to require building and formatting code after making changes, addressing issues where Copilot was generating code with build or formatting errors.

Changes:

• Added instruction to run dotnet build after adding, modifying, or deleting code
• Added instruction to run dotnet format after adding or modifying code

[Copilot]

The first instruction mentions "After adding, modifying or deleting code, run dotnet build" but the second instruction only mentions "After adding or modifying code, run dotnet format". This inconsistency is noticeable - if formatting should be run after deletion as well, it should be included; if not, the reasoning should be clear. Consider making these consistent, likely by including "deleting" in the second instruction as well, since deleting code could also affect formatting (e.g., removing code might leave trailing whitespace or empty lines that need formatting).

Suggested change

	- After adding or modifying code, run `dotnet format` to automatically fix any formatting errors.
	- After adding, modifying or deleting code, run `dotnet format` to automatically fix any formatting errors.