Make Fleet tests sync + async, add ManagedNamespace test support

[frantran]

Make Fleet tests sync + async, add ManagedNamespace test support

addresses the issues here: #56483 (comment)

[Copilot]

Pull request overview

Updates the Azure ResourceManager ContainerServiceFleet SDK to expand scenario coverage and adjust long-running operation (LRO) polling behavior, in support of the Fleet API version 2025-08-01-preview and the feedback noted in the referenced PR discussion.

Changes:

• Run the Fleet CRUD scenario test suite in both “async” and “sync” fixture modes and update Fleet create payload to include HubProfile.DnsPrefix.
• Add scenario coverage for Fleet Managed Namespace CRUD operations.
• Change Fleet-specific generated LRO operation defaults around skipApiVersionOverride, and update the assets tag.

Reviewed changes

Copilot reviewed 2 out of 4 changed files in this pull request and generated 9 comments.

File	Description
sdk/fleet/Azure.ResourceManager.ContainerServiceFleet/tests/Scenario/FleetCRUD.cs	Adds dual-fixture execution and extends scenario coverage with Managed Namespace CRUD operations and Fleet hub profile settings.
sdk/fleet/Azure.ResourceManager.ContainerServiceFleet/src/Generated/LongRunningOperation/ContainerServiceFleetArmOperationOfT.cs	Changes default skipApiVersionOverride behavior for generic Fleet LRO polling.
sdk/fleet/Azure.ResourceManager.ContainerServiceFleet/src/Generated/LongRunningOperation/ContainerServiceFleetArmOperation.cs	Changes default skipApiVersionOverride behavior for non-generic Fleet LRO polling.
sdk/fleet/Azure.ResourceManager.ContainerServiceFleet/assets.json	Updates the recorded assets tag reference.