Fix resource leaks in DurableTaskSchedulerWorkerExtensionsTests

[Copilot]

ServiceProvider instances in test methods were not being disposed, causing gRPC channel handle leaks across test runs.

Changes

• Updated 8 test methods to use await using for ServiceProvider disposal
• Changed affected test signatures from void to async Task
• Refactored two tests that verify disposal behavior to use scoped using blocks

Example

Before:

[Fact]
public void UseDurableTaskScheduler_WithEndpointAndCredential_ShouldConfigureCorrectly()
{
    // ...
    ServiceProvider provider = services.BuildServiceProvider();
    // provider never disposed
}

After:

[Fact]
public async Task UseDurableTaskScheduler_WithEndpointAndCredential_ShouldConfigureCorrectly()
{
    // ...
    await using ServiceProvider provider = services.BuildServiceProvider();
    // automatically disposed when scope exits
}

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.