Fix public build ci not picking up latest built test assembly

[YunchuWang]

This PR addresses an issue where the VSTest@2 task fails to pick up the latest built test assemblies when running in distributed agent mode.

Without this fix, the test discovery phase uses the most recently built DLLs to detect and assign test cases. However, during execution, the distributed agents may use stale, cached test assemblies from previous successful pipeline runs—potentially missing newly added test cases.

This change ensures that all test agents receive the latest built test DLLs, preventing "test not found" errors and guaranteeing accurate test discovery and execution.

Relevant documentation:
https://learn.microsoft.com/en-us/azure/devops/pipelines/tasks/reference/vstest-v2?view=azure-pipelines

Test artifact handling and publishing:

• Updated testAssembly paths in eng/ci/public-build.yml to use a unified directory structure (tests/**) and added artifactName parameters for each test stage to specify artifact names (CoreTests, AzureStorageTests, EmulatorTests). [1] [2] [3]
• Added steps in eng/templates/build-steps.yml to publish test artifacts (CoreTests, AzureStorageTests, EmulatorTests) using the 1ES.PublishPipelineArtifact task. [1] [2] [3]

Test execution improvements:

• Enhanced eng/templates/test.yml to include a new artifactName parameter and steps for downloading test artifacts and listing downloaded test DLLs.
• Updated the testAssemblyVer2 parameter to use the downloaded artifact path for test execution.
• Enabled parallel test execution with the runInParallel option for the VSTest task.