feat: added remote API module

[petruki]

This pull request introduces significant improvements to the feature flag client, focusing on enhanced remote evaluation support, improved error handling, and updated documentation and tests to reflect these changes. The core logic for remote criteria evaluation has been added, along with new error types and result handling structures. The usage examples and tests have been updated to use the new error-aware API.

Remote criteria evaluation and error handling:

• Added remote.go with logic for remote criteria evaluation, including token management, criteria checks, and HTTP client configuration. This enables secure and robust remote feature flag evaluation.
• Introduced structured error types in errors.go (RemoteError, RemoteAuthError, RemoteCriteriaError) for clearer error management during remote operations.
• Added ResultDetail struct in result.go to encapsulate detailed results of feature evaluation, including metadata and reasons.

Switcher API enhancements:

• Updated Switcher methods in switcher.go to support error returns: IsOn() and IsOnWithDetails() now return errors, and new methods like CheckValue, Prepare, and appendFilteredEntries provide more flexible criteria management.
• Added new fields to Client for authentication token management.

Documentation and test updates:

• Updated all usage examples in README.md to handle errors returned by IsOn() and related methods, ensuring best practices are followed in client usage.
• Enhanced tests in switcher_test.go to cover new error scenarios, token preparation, and entry filtering logic.

These changes collectively make the client more robust, secure, and user-friendly, especially in remote and error-prone environments.

[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

See analysis details on SonarQube Cloud