Don't throw from component telemetry context dispose if not initialized

[JamesNK]

Description

I noticed that ComponentTelemetryContext.Dispose() would throw if called without the context being initialized. This could happen if there is an error in a component before initialization and then the context is dispose with the component.

It's a bug but not a critical one. Requires other things to go wrong first.

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
    • Link to aspire-docs issue (consider using one of the following templates):
      • New (or update) doc-idea template
      • New breaking-change template
      • New diagnostic template
  • No

[Copilot]

Pull Request Overview

This PR ensures that disposing a ComponentTelemetryContext without prior initialization does not throw an exception. The changes include:

• Updated test cases to cover telemetry enabled, telemetry disabled, and disposal without initialization scenarios.
• Modified ComponentTelemetryContext to use a safe-call operator in Dispose, preventing exceptions when the telemetry service is unassigned.

Reviewed Changes

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

File	Description
tests/Aspire.Dashboard.Tests/Telemetry/ComponentTelemetryContextTests.cs	Added test coverage for disposal behavior with and without telemetry enabled.
src/Aspire.Dashboard/Components/Pages/ComponentTelemetryContext.cs	Altered property access and disposal logic to safely handle uninitialized telemetry service.