[dotnet] Add SystemClock singleton

[RenderMichael]

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Add SystemClock singleton

Motivation and Context

This minimizes an allocation when using the WebDriverWait type, and adjacent types like components and waits

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

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PR Type

Enhancement, Tests

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Description

• Introduced a singleton SystemClock.Instance to minimize allocations.

• Updated various classes to use SystemClock.Instance instead of creating new instances.

• Refactored FakeClock to HandCrankClock with improved naming and functionality.

• Adjusted related tests to align with the new SystemClock.Instance and HandCrankClock.

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Changes walkthrough 📝

	Relevant files
Enhancement	PopupWindowFinder.cs Use `SystemClock.Instance` in `PopupWindowFinder`                dotnet/src/support/UI/PopupWindowFinder.cs Replaced new SystemClock() with SystemClock.Instance. Simplified WebDriverWait initialization. +1/-1      SlowLoadableComponent{T}.cs Use `SystemClock.Instance` in `SlowLoadableComponent`        dotnet/src/support/UI/SlowLoadableComponent{T}.cs Replaced new SystemClock() with SystemClock.Instance. Updated constructor for consistency. +1/-1      DefaultWait{T}.cs Use `SystemClock.Instance` in `DefaultWait`                            dotnet/src/webdriver/Support/DefaultWait{T}.cs Replaced new SystemClock() with SystemClock.Instance. Simplified constructor logic. +1/-1      SystemClock.cs Introduce singleton instance for `SystemClock`                      dotnet/src/webdriver/Support/SystemClock.cs Added SystemClock.Instance as a singleton instance. Ensured thread-safe initialization. +5/-0      WebDriverWait.cs Use `SystemClock.Instance` in `WebDriverWait`                        dotnet/src/webdriver/Support/WebDriverWait.cs Replaced new SystemClock() with SystemClock.Instance. Updated constructor for consistency. +1/-1      HandCrankClock.cs Refactor `FakeClock` to `HandCrankClock`                                  dotnet/test/support/UI/HandCrankClock.cs Renamed FakeClock to HandCrankClock. Improved method naming for clarity. Simplified property and method implementations. +3/-12
Tests	SlowLoadableComponentTest.cs Update tests for `SystemClock` and `HandCrankClock`            dotnet/test/support/UI/SlowLoadableComponentTest.cs Updated tests to use SystemClock.Instance. Replaced FakeClock with HandCrankClock. Adjusted test logic to align with new clock implementation. +10/-14

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PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

⏱️ Estimated effort to review: 2 🔵🔵⚪⚪⚪

🧪 PR contains tests

🔒 No security concerns identified

⚡ Recommended focus areas for review Thread Safety The SystemClock singleton instance is initialized using an auto-property. Consider using explicit thread-safe initialization pattern like lazy initialization to ensure thread safety. public static SystemClock Instance { get; } = new(); Naming Clarity The variable name 'fakeNow' could be renamed to something more descriptive like 'currentTime' or 'simulatedTime' to better reflect its purpose in the test clock implementation. private DateTime fakeNow = new DateTime(50000);

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PR Code Suggestions ✨

Explore these optional code suggestions:

Category	Suggestion	Impact
General	Enforce singleton pattern implementation Add a private constructor to prevent direct instantiation of SystemClock since it's designed as a singleton. This enforces the singleton pattern and prevents potential multiple instances. dotnet/src/webdriver/Support/SystemClock.cs [29-34] public class SystemClock : IClock { /// <summary> /// An instance of the <see cref="SystemClock"/> type. /// </summary> public static SystemClock Instance { get; } = new(); + private SystemClock() { } + Apply this suggestion Suggestion importance[1-10]: 7 __ Why: Adding a private constructor is a good practice to properly implement the singleton pattern, preventing accidental instantiation and ensuring better encapsulation of the SystemClock class.	Medium

[RenderMichael]

SystemClock is a stateless type, and it gets initialized each time a WebDriverWait is created. This can remove an intermediate allocation from a commonly-used type.

[nvborisenko]

Thanks, micro-optimizations are always good, even if it is nano :) I concern this approach will not work if in future we will add parameter in ctor. But I cannot image which one might be added.

[RenderMichael]

If we add a parameter in the constructor, then users who use new SystemClock() will be broken too!

The only reason users may be forced to care about the SystemClock (or the IClock interface in general) is if they want a custom sleep interval. We do not have a constructor in WebDriverWait which lets you specify a sleep interval without an IClock too.

For that reason, I opened #15314 👀