.NET: Cosmos DB UT Fast Skip (For Non-Configured Local envs)

[rogerbarreto]

Motivation and Context

Cosmos DB Unit Tests do not fail fast when the environment is not configured.

This change solves this making the whole project skip at once for non-configured environments.

This change also skip Emulator running in every single pipeline when no CosmosDB code related was changed, improving execution the time.

[Copilot]

Pull request overview

This PR implements fast-fail behavior for Cosmos DB unit tests when the emulator is not available and optimizes CI pipeline execution by conditionally starting the Cosmos DB emulator only when CosmosDB-related code changes are detected.

Key changes:

• Added SkipIfEmulatorNotAvailable() calls in test initialization to enable fast skipping when the emulator is not configured
• Introduced path filtering for CosmosDB changes to conditionally start the emulator in CI pipelines
• Added COSMOS_EMULATOR_AVAILABLE environment variable to signal emulator availability to tests

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
dotnet/tests/Microsoft.Agents.AI.CosmosNoSql.UnitTests/CosmosCheckpointStoreTests.cs	Added fast-skip check in InitializeAsync() and removed unnecessary using Xunit; statement
dotnet/tests/Microsoft.Agents.AI.CosmosNoSql.UnitTests/CosmosChatMessageStoreTests.cs	Added fast-skip check in InitializeAsync() and removed unnecessary using Xunit; statement
.github/workflows/dotnet-build-and-test.yml	Added CosmosDB path filter, conditional emulator startup, and COSMOS_EMULATOR_AVAILABLE environment variable configuration