Add feature flag evaluation context parity #188

Summary

Add missing feature flag evaluation context parity to the Ruby SDK.

Specs

• sdk-specs/openspec/specs/get-feature-flag/spec.md
• sdk-specs/openspec/specs/is-feature-enabled/spec.md
• sdk-specs/openspec/specs/local-feature-flag-evaluator/spec.md

Current evidence

The SDK audit found that flag APIs lack device_id; legacy/bulk APIs also lack some newer context options.

Expected behavior

• Allow passing device_id through relevant feature flag evaluation APIs.
• Use device_id in local/remote evaluation where required by the flag definition/evaluation context.
• Bring legacy and bulk flag APIs closer to the canonical server-side context options where applicable.
• Add tests for remote request body propagation and local evaluation bucketing/context behavior.