Improve command notification to show result if toast has closed

[JamesNK]

Description

This is the dashboard UI changes from - #6625. The server changes in that PR need work, but the dashboard UI stuff can be improved now.

When a command is started a toast is immediately shown. It is open for 5 seconds. When the command is finished the toast is updated to show the result.

Previously if the toast had closed because it ran for more than 5 seconds then the UI wouldn't display the result. This PR improves logic so that if the original toast is still open then it is updated and kept open longer. And if it is closed then a new toast is displayed.

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Is this introducing a breaking change?
      • Yes
        • Link to aspire-docs issue (please use this breaking-change template):
      • No
        • Link to aspire-docs issue (please use this doc-idea template):
  • No

[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated no suggestions.

Comments skipped due to low confidence (1)

src/Aspire.Dashboard/Model/DashboardCommandExecutor.cs:33

• The new behavior for handling toast display and closing should be covered by tests to ensure it works as expected.

// When a resource command starts a toast is immediately shown.