Better caching

[JonathanBout]

This pull request includes several changes to the SimpleCDN project, focusing on enhancing test coverage, refactoring code, and improving the caching mechanism. The most important changes include the addition of new tests, refactoring of existing test files, and the introduction of mock classes for testing purposes.

Test Enhancements:

• SimpleCDN.Tests/CacheManagerTests.cs: Added new test cases to verify the functionality of the CacheManager class, including tests for adding, removing, and checking the existence of cached files.
• SimpleCDN.Tests/CachedFileBinarizationTests.cs: Introduced new tests to validate the serialization and deserialization of CachedFile objects.

Refactoring and Code Simplification:

• SimpleCDN.Tests/CDNLoaderTests.cs: Refactored the CDNLoaderTests class to use a dictionary for mock files, simplifying the setup and teardown processes. Also added new test cases for path traversal scenarios. [1] [2] [3] [4]
• SimpleCDN/Cache/CachedFile.cs: Changed the Size property from long to int and added methods for serializing and deserializing CachedFile objects. [1] [2]

Introduction of Mock Classes:

• SimpleCDN.Tests/Mocks/DistributedCacheMock.cs: Added a mock implementation of the IDistributedCache interface for testing purposes.
• SimpleCDN.Tests/Mocks/MockCacheManager.cs: Created a mock implementation of the ICacheManager interface to facilitate testing of cache-related functionality.
• SimpleCDN.Tests/Mocks/MockPhysicalFileReader.cs: Implemented a mock version of the IPhysicalFileReader interface to simulate file reading operations during tests.

These changes collectively enhance the robustness and maintainability of the SimpleCDN project by improving test coverage and simplifying the codebase.