feat: added built-in mocking feature

[petruki]

This pull request introduces a comprehensive client-scoped mocking system to the Go SDK for Switcher, allowing feature flag results to be overridden in tests with fine-grained control. It adds a fluent API for defining mocks, conditional mocking based on strategies, metadata attachment, and automatic cleanup integration with Go's testing framework. The changes are well-documented in the README and thoroughly tested.

Mocking and Testability Enhancements:

• Added a new mocking system to the Client via the Assume and Forget methods, allowing test code to override feature flag results per client instance. The fluent API supports forced true/false, conditional mocks based on strategies, metadata, and automatic cleanup registration. (mock.go, client.go, [1] [2] [3]
• Integrated the mocking system into the main evaluation flow: Switcher.submit now checks for mocked results before normal evaluation. (switcher.go, switcher.goR180-R185)
• Added a comprehensive test suite for the mocking system, covering forced results, conditional logic, metadata, cleanup, and interaction with the snapshot system. (mock_test.go, mock_test.goR1-R184)

Documentation Updates:

• Updated the README to document the new mocking API, provide usage examples, and clarify that mocks are client-scoped. Removed outdated references to "Test Helpers (Under development)" and clarified the focus on mocking. (README.md, [1] [2] [3] [4]

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

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