(#217) Added dynamic proxies tests, plus some Cosmos test fixes.

[adrianhall]

Closes #217

PR Overview

This PR adds additional tests for dynamic proxies and Cosmos DB integration while refactoring and cleaning up unused usings.

• Added tests for dynamic proxies to validate offline context behavior.
• Introduced new Cosmos Table Data tests and refactored the PackedKeyOptions for improved ID parsing.
• Removed unused using directives across several files to improve clarity.

Reviewed Changes

File	Description
tests/CommunityToolkit.Datasync.Server.CosmosDb.Test/CosmosTableData_Tests.cs	Adds tests for Cosmos table data conversion and equality.
tests/CommunityToolkit.Datasync.Client.Test/Offline/DynamicProxies_Tests.cs	Introduces tests to verify dynamic proxy support in offline database operations.
tests/CommunityToolkit.Datasync.Server.CosmosDb.Test/Options/PackedKeyOptions.cs	Refactors the options class with concise constructor syntax and updates ID parsing.
tests/CommunityToolkit.Datasync.Server.CosmosDb.Test/PackedKeyRepository_Tests.cs	Updates ID parsing logic and removes unused using directives.
tests/CommunityToolkit.Datasync.Server.CosmosDb.Test/CosmosDbRepository_Tests.cs	Removes unused using directives and applies minor formatting adjustments.
src/CommunityToolkit.Datasync.Server.CosmosDb/CosmosTableData.cs	Removes unused using directives.
tests/CommunityToolkit.Datasync.Server.CosmosDb.Test/Models/CosmosDbMovie.cs	Cleans up redundant using directives.

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (2)

tests/CommunityToolkit.Datasync.Server.CosmosDb.Test/Options/PackedKeyOptions.cs:30

• [nitpick] Consider providing more context in the exception message for failed ID parsing (e.g., include the invalid input) to aid debugging.

if (!int.TryParse(parts[1], out int year))

tests/CommunityToolkit.Datasync.Server.CosmosDb.Test/CosmosTableData_Tests.cs:18

• [nitpick] The class name 'CCosmosTableData' may be unclear; consider renaming it to a more descriptive identifier (e.g., 'TestCosmosTableData').

CCosmosTableData entity_a = a.ToTableEntity<CCosmosTableData>();