feat: add Stopwatch support to ITimeSystem

[vbreuss]

Adds a System.Diagnostics.Stopwatch abstraction to ITimeSystem, enabling both RealTimeSystem and MockTimeSystem consumers to create/use stopwatches through a testable interface.

Key Changes:

• Introduces IStopwatch and IStopwatchFactory and wires them into ITimeSystem, RealTimeSystem, and MockTimeSystem.
• Implements real wrappers (StopwatchFactory/StopwatchWrapper) and mock implementations (StopwatchFactoryMock/StopwatchMock), plus parity and unit tests.
• Adds a feature flag for Stopwatch.GetElapsedTime (.NET 8 or higher)
• Adjusts build/project configuration (conditional PackageReference vs ProjectReference for the Interface project, pipeline + versioning tweaks).

[github-actions]

Test Results

 1 files   -      51   1 suites   - 51   0s ⏱️ - 36m 1s
13 tests  -  64 419  12 ✅  -  60 805  1 💤  -  3 614  0 ❌ ±0 
13 runs   - 133 311  12 ✅  - 118 768  1 💤  - 14 543  0 ❌ ±0 

Results for commit 1252944. ± Comparison against base commit 0ba083b.

♻️ This comment has been updated with latest results.

[Copilot]

Pull request overview

Adds a System.Diagnostics.Stopwatch abstraction to ITimeSystem, enabling both RealTimeSystem and MockTimeSystem consumers to create/use stopwatches through a testable interface.

Changes:

• Introduces IStopwatch and IStopwatchFactory and wires them into ITimeSystem, RealTimeSystem, and MockTimeSystem.
• Implements real wrappers (StopwatchFactory/StopwatchWrapper) and mock implementations (StopwatchFactoryMock/StopwatchMock), plus parity and unit tests.
• Adjusts build/project configuration (conditional PackageReference vs ProjectReference for the Interface project, feature flag for Stopwatch.GetElapsedTime, pipeline + versioning tweaks).

Reviewed changes

Copilot reviewed 28 out of 28 changed files in this pull request and generated 16 comments.

Show a summary per file

File	Description
Tests/Testably.Abstractions.Tests/TimeSystem/StopwatchTests.cs	New time-system tests for IStopwatch behavior.
Tests/Testably.Abstractions.Tests/TimeSystem/StopwatchFactoryTests.cs	New tests for IStopwatchFactory static-like members and GetElapsedTime (feature-gated).
Tests/Testably.Abstractions.Tests/Testably.Abstractions.Tests.csproj	Debug uses Interface ProjectReference; non-Debug uses PackageReference.
Tests/Testably.Abstractions.Testing.Tests/TimeSystem/StopwatchMockTests.cs	New mock-specific precision test for tick-based elapsed behavior.
Tests/Testably.Abstractions.Testing.Tests/Testably.Abstractions.Testing.Tests.csproj	Debug uses Interface ProjectReference; non-Debug uses PackageReference.
Tests/Testably.Abstractions.Parity.Tests/Testably.Abstractions.Parity.Tests.csproj	Debug uses Interface ProjectReference; non-Debug uses PackageReference; refactors Compression reference group.
Tests/Testably.Abstractions.Parity.Tests/TestHelpers/Parity.cs	Adds parity configuration for Stopwatch comparisons.
Tests/Testably.Abstractions.Parity.Tests/ParityTests.cs	Adds parity test for IStopwatch/IStopwatchFactory vs System.Diagnostics.Stopwatch.
Tests/Helpers/Testably.Abstractions.TestHelpers/Testably.Abstractions.TestHelpers.csproj	Debug uses Interface ProjectReference; non-Debug uses PackageReference.
Source/Testably.Abstractions/TimeSystem/TimerFactory.cs	Fixes incorrect <inheritdoc> cref for Wrap(Timer).
Source/Testably.Abstractions/TimeSystem/StopwatchWrapper.cs	New real wrapper implementing IStopwatch.
Source/Testably.Abstractions/TimeSystem/StopwatchFactory.cs	New real factory implementing IStopwatchFactory.
Source/Testably.Abstractions/Testably.Abstractions.csproj	Debug uses Interface ProjectReference; non-Debug uses PackageReference.
Source/Testably.Abstractions/RealTimeSystem.cs	Adds Stopwatch factory property and initialization.
Source/Testably.Abstractions.Testing/TimeSystem/TimerFactoryMock.cs	Fixes incorrect <inheritdoc> cref for Wrap(Timer).
Source/Testably.Abstractions.Testing/TimeSystem/StopwatchMock.cs	New mock stopwatch implementation based on mocked time provider.
Source/Testably.Abstractions.Testing/TimeSystem/StopwatchFactoryMock.cs	New mock stopwatch factory implementing IStopwatchFactory.
Source/Testably.Abstractions.Testing/Testably.Abstractions.Testing.csproj	Debug uses Interface ProjectReference; non-Debug uses PackageReference.
Source/Testably.Abstractions.Testing/MockTimeSystem.cs	Adds Stopwatch property; renames internal timer factory field for clarity.
Source/Testably.Abstractions.Testing/Helpers/ExceptionFactory.cs	Adds NotSupported exception factory for stopwatch wrapping in mock.
Source/Testably.Abstractions.Interface/TimeSystem/IStopwatchFactory.cs	New public stopwatch factory abstraction.
Source/Testably.Abstractions.Interface/TimeSystem/IStopwatch.cs	New public stopwatch abstraction.
Source/Testably.Abstractions.Interface/ITimeSystem.cs	Adds Stopwatch property to the time system abstraction.
Source/Testably.Abstractions.Compression/Testably.Abstractions.Compression.csproj	Debug uses Interface ProjectReference; non-Debug uses PackageReference.
Source/Testably.Abstractions.AccessControl/Testably.Abstractions.AccessControl.csproj	Debug uses Interface ProjectReference; non-Debug uses PackageReference.
Source/Directory.Build.props	Sets a local build Version fallback (intended to be overridden in pipeline).
Pipeline/Build.cs	Changes default BuildScope (affects CI target gating).
Feature.Flags.props	Adds FEATURE_STOPWATCH_GETELAPSEDTIME for net8+.

[github-actions]

This is addressed in release v5.3.0.