feat: added local snapshot resolver

[petruki]

This pull request introduces local snapshot support for evaluating feature switches, enabling offline and deterministic switcher evaluations based on local JSON files. It adds snapshot loading, local criteria evaluation logic, new error types, and comprehensive tests to ensure correctness for various scenarios.

Snapshot support and local evaluation:

• Added a Snapshot struct and related types in snapshot.go to represent local feature state, with logic for loading, creating, and reading snapshot files.
• Implemented snapshot loading and version tracking in the Client struct and provided new methods: LoadSnapshot, SnapshotVersion, and internal state management for snapshots in client.go. [1] [2]
• Introduced local criteria evaluation logic in resolver.go to determine switcher state based on the loaded snapshot, supporting value and network strategies, group and config activation, and relay restrictions.
• Updated the Switcher logic in switcher.go to use local snapshot evaluation when in local mode, added support for network-based criteria, and improved criteria entry handling. [1] [2] [3] [4]

Error handling:

• Added a new LocalCriteriaError type in errors.go to distinguish local evaluation errors from remote errors, with corresponding error construction helpers.

Testing:

• Added a comprehensive test suite in local_test.go covering snapshot loading, error cases, and various switcher evaluation scenarios using local snapshots.

[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