[V4] Update DynamoDB tests to use async operations

[dscpinheiro]

Another follow-up for #4178, this updates the DDB .NET Framework integration tests to use async operations when possible. I tried to split one file in each commit to make the review more manageable.

Testing

• Dry-run: DRY_RUN-82596693-e13f-425a-9515-31a47d1cc7f6

License

• I confirm that this pull request can be released under the Apache 2 license

[dscpinheiro]

This class is not marked with the TestClass attribute so the test never runs... I deleted it since it wasn't doing anything special, we have a separate project for CSM tests: https://github.com/aws/aws-sdk-net/tree/main/sdk/test/CSMTest

[dscpinheiro]

ReuseTables is hard-coded to true so this test is always skipped. Also deleted since several other tests call Create / DeleteTable themselves.

[Copilot]

Pull request overview

This pull request updates DynamoDB .NET Framework integration tests to use async operations consistently throughout the codebase. The changes follow up on PR #4178 and modernize the test suite by:

• Converting synchronous DynamoDB operations to their async counterparts
• Updating test method signatures from void/Task to async Task
• Replacing synchronous exception assertions with async-compatible patterns
• Modernizing code patterns (e.g., Thread.Sleep → Task.Delay, yield return → collection building)

Key Changes

• Async operation adoption: All DynamoDB CRUD operations (Save, Load, Query, Scan, etc.) now use async methods with proper await
• Test infrastructure updates: ClassInitialize, ClassCleanup, and TestCleanup methods updated to async
• Exception handling: Migrated from AssertExtensions.ExpectException to Assert.ThrowsExceptionAsync

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
TTLTests.cs	Converted TTL-related test methods to async, updated Context operations and document table operations
ServiceTests.cs	Converted service layer tests to async, refactored ScanHelper from yield return to collection-based approach
JSONTests.cs	Updated JSON document tests with async operations and inline document initialization
DynamoDBTestsBase.cs	Converted base test infrastructure (setup/teardown) to async, added parallel cleanup with Task.WhenAll
DocumentTests.cs	Comprehensive async conversion of document operations, replaced Thread.Sleep with Task.Delay
DataModelTests.cs	Converted DataModel context operations to async, updated query/scan operations
Cache.cs	Updated cache tests to async, added NETFRAMEWORK conditional compilation
CSMTest.cs	Removed deprecated test file
AWSSDK.IntegrationTests.DynamoDBv2.NetFramework.csproj	Added CS0618 to NoWarn to suppress obsolete API warnings