feat: implement mock PeriodicTimer in testing package

[vbreuss]

Adds PeriodicTimer support to the ITimeSystem abstraction by introducing a mock implementation in Testably.Abstractions.Testing, plus tests and API-surface updates to validate/lock in the new contract.

Key Changes:

• Implement PeriodicTimerMock + PeriodicTimerFactoryMock and expose them via MockTimeSystem.PeriodicTimer (feature-flagged).
• Add test coverage for PeriodicTimer factory and timer behavior under TimeSystemTests.
• Update API expectation files and add the aweXpect.Chronology test dependency; adjust build/package config.

--

• Part of Add support for PeriodicTimer in ITimeSystem #960

[Copilot]

Pull request overview

Adds PeriodicTimer support to the ITimeSystem abstraction by introducing a mock implementation in Testably.Abstractions.Testing, plus tests and API-surface updates to validate/lock in the new contract.

Changes:

• Implement PeriodicTimerMock + PeriodicTimerFactoryMock and expose them via MockTimeSystem.PeriodicTimer (feature-flagged).
• Add test coverage for PeriodicTimer factory and timer behavior under TimeSystemTests.
• Update API expectation files and add the aweXpect.Chronology test dependency; adjust build/package config.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
Tests/Testably.Abstractions.Tests/TimeSystem/PeriodicTimerTests.cs	Adds behavior tests for IPeriodicTimer across time systems.
Tests/Testably.Abstractions.Tests/TimeSystem/PeriodicTimerFactoryTests.cs	Adds validation + period propagation tests for the factory.
Tests/Testably.Abstractions.Testing.Tests/TimeSystem/PeriodicTimerFactoryMockTests.cs	Ensures wrapping an existing PeriodicTimer is rejected in MockTimeSystem.
Tests/Directory.Build.props	Adds aweXpect.Chronology reference for duration extensions in tests.
Tests/Api/Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_net8.0.txt	Updates expected API surface (MockTimeSystem.PeriodicTimer).
Tests/Api/Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_net9.0.txt	Updates expected API surface (MockTimeSystem.PeriodicTimer).
Tests/Api/Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_net10.0.txt	Updates expected API surface (MockTimeSystem.PeriodicTimer).
Source/Testably.Abstractions.Testing/TimeSystem/PeriodicTimerMock.cs	Implements mock IPeriodicTimer behavior.
Source/Testably.Abstractions.Testing/TimeSystem/PeriodicTimerFactoryMock.cs	Implements mock IPeriodicTimerFactory for MockTimeSystem.
Source/Testably.Abstractions.Testing/MockTimeSystem.cs	Wires PeriodicTimer factory into MockTimeSystem behind feature flag.
Source/Testably.Abstractions.Testing/Helpers/ExceptionFactory.cs	Adds NotSupportedPeriodicTimerWrapping and minor formatting changes.
README.md	Documents PeriodicTimer as a supported abstraction.
Pipeline/Build.cs	Resets build scope to default.
Directory.Packages.props	Adds aweXpect.Chronology version + bumps internal package versions.

[github-actions]

Test Results

    102 files  +    101      102 suites  +101   3h 4m 3s ⏱️ + 3h 4m 1s
112 447 tests +112 435   99 844 ✅ + 99 832  12 603 💤 +12 603  0 ❌ ±0 
267 786 runs  +267 774  231 288 ✅ +231 276  36 498 💤 +36 498  0 ❌ ±0 

Results for commit f1804f6. ± Comparison against base commit fd3a7ab.

♻️ This comment has been updated with latest results.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
96.2% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

This is addressed in release v6.0.0.