fix(tests): Fix flaky tests and add reusable test infrastructure

[currantw]

Summary

• Fix flaky integration tests:
  • TestKeyIdleTime
  • UpdateConnectionPasswordTests
  • ReadFromTests.ConfigurationPipeline_ClonePreservesReadFromConfiguration
  • ReadFromTests.ConfigurationPipeline_ValidationErrorPropagation
• Introduce reusable test infrastructure including a Polling utility and ServerFixture base class.

Issue Link

• Closes [C#][Flaky Test] GenericCommandTests.TestKeyIdleTime(client: GlideClient { 0x7F83DC00CFA0 RESP2 }) #94
• Closes [C#][Flaky Test] UpdateConnectionPasswordTests.UpdateConnectionPassword_Cluster_ImmediateAuth #143

Features and Behaviour Changes

⚪ None — test infrastructure only.

Implementation

• Test infrastructure:
  • New Polling utility (tests/Valkey.Glide.TestUtils/Polling.cs): Provides AssertTrue and AssertTrueAsync methods that poll a condition with configurable timeout and interval, calling Assert.Fail on timeout. Follows the same pattern previously used in PubSubUtils.
  • New ServerFixture base class (tests/Valkey.Glide.TestUtils/Fixture.cs): Provides shared standalone/cluster servers, GetServer(bool), CreateClientAsync(bool), and IDisposable lifecycle for test fixtures that need isolated servers.
• Flaky test fixes:
  • Fix TestKeyIdleTime: Replaced the fixed 1-second Task.Delay with a polling loop that retries for up to 10 seconds.
  • Fix UpdateConnectionPasswordTests: Introduced UpdateConnectionPasswordFixture (extends ServerFixture) with a RetryStrategy for cluster client creation to handle transient connection timeouts during cluster startup. Replaced [InlineData(true/false)] with [MemberData(nameof(ClusterMode), MemberType = typeof(Data))]. Servers are now shared via the fixture instead of created per-test.
  • Fix ReadFromTests: Use TestConfiguration.DefaultCompatibleConfig() instead of manual ConfigurationOptions setup in ConfigurationPipeline_ValidationErrorPropagation and ConfigurationPipeline_ClonePreservesReadFromConfiguration, ensuring ResponseTimeout is set to prevent timeouts in CI.
• Refactoring
  • Refactored existing polling loops: Updated PubSubUtils.AssertSubscribedAsync, PubSubUtils.AssertNotSubscribedAsync, PubSubQueueTests, and PubSubCommandTests.AssertHandlerReceives to use the new Polling utility, reducing duplicated boilerplate.

Limitations

⚪ None

Testing

✅ All tests pass (dotnet build with zero warnings/errors).

Related Issues

• [C#][Flaky Test] GenericCommandTests.TestKeyIdleTime(client: GlideClient { 0x7F83DC00CFA0 RESP2 }) #94 (flaky TestKeyIdleTime)
• [C#][Flaky Test] UpdateConnectionPasswordTests.UpdateConnectionPassword_Cluster_ImmediateAuth #143 (flaky UpdateConnectionPassword cluster mode)

Checklist

• This Pull Request is related to one issue.
• Commit message has a detailed description of what changed and why.
• Tests are added or updated and all checks pass.
• CHANGELOG.md, README.md, DEVELOPER.md, and other documentation files are updated.
• Destination branch is correct - main or release
• Create merge commit if merging release branch into main, squash otherwise.