Rename CommunityToolkit.VectorData.CosmosNoSql to AzureCosmosDB

[Copilot]

Motivation & Context

CommunityToolkit renamed the CommunityToolkit.VectorData.CosmosNoSql package to CommunityToolkit.VectorData.AzureCosmosDB (see CommunityToolkit/AI#48), which also renamed CosmosNoSqlVectorStore to CosmosVectorStore. This PR updates all references in the repo to track the new package and type names.

Description & Review Guide

• What are the major changes?
  • Directory.Packages.props: CommunityToolkit.VectorData.CosmosNoSql → CommunityToolkit.VectorData.AzureCosmosDB.
  • Bumped Microsoft.Extensions.VectorData.Abstractions from 10.7.0 → 10.8.2, the new minimum required by CommunityToolkit.VectorData.AzureCosmosDB 1.0.0.
  • AgentWithMemory_Step08_MemoryUsingCosmosNoSql sample: updated PackageReference, using directive, and renamed CosmosNoSqlVectorStore/CosmosNoSqlVectorStoreOptions → CosmosVectorStore/CosmosVectorStoreOptions in Program.cs, plus the corresponding type name in the sample README.md.
• What is the impact of these changes?
  • No behavioral change; this is a mechanical rename to keep the sample compiling against the current CommunityToolkit package.
• What do you want reviewers to focus on?
  • Confirm no other project (e.g. the unrelated Microsoft.Agents.AI.CosmosNoSql first-party integration) was mistakenly touched — it does not depend on the CommunityToolkit package and was left as-is.
  • Confirm the Microsoft.Extensions.VectorData.Abstractions version bump doesn't affect other consumers (only Microsoft.Agents.AI references it, and it builds clean).

// Before
using CommunityToolkit.VectorData.CosmosNoSql;
VectorStore vectorStore = new CosmosNoSqlVectorStore(database, new CosmosNoSqlVectorStoreOptions { ... });

// After
using CommunityToolkit.VectorData.AzureCosmosDB;
VectorStore vectorStore = new CosmosVectorStore(database, new CosmosVectorStoreOptions { ... });

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) — a workflow keeps the label and title prefix in sync automatically.