feat(flags): add rules engine boundary (FFL-2837 PR1)

[btthomas]

Pull request stack

1. Plan PR (#1345)
2. PR1: Rules engine boundary (feat(flags): add rules engine boundary (FFL-2837 PR1) #1346) <- you are here
3. PR2: Dynamic offline evaluation (#1347)
4. PR3: Provider API and documentation (#1348)

Summary

This PR adds the internal boundary for dynamic offline rule evaluation.

• It adds one adapter for the flagging-core rules engine.
• It converts SDK contexts to flat rules contexts.
• It preserves the difference between a missing targeting key and an empty targeting key.
• It clones and freezes the temporary rules configuration.
• It omits an invalid flag without removing valid sibling flags.
• It normalizes evaluation results.
• It rejects serialization when a configuration contains rules.
• It adds rules-wire and adapter contract tests.
• It does not change FlagsClient or provider behavior.

Reason

The React Native SDK must not implement a second rules engine. The adapter keeps flagging-core details out of the SDK state machine. Tests can replace the adapter with a deterministic fake.

Temporary upstream code

The latest published flagging-core version is 2.0.2. It does not contain the rules wire and protobuf evaluator from openfeature-js-client#344.

This PR has three TODO(FFL-2837) items:

• Delete the legacy JSON rules-wire compatibility shim after PR Add Support for RN 0.71 #344 is published.
• Delete the temporary JSON clone and validator after PR Add Support for RN 0.71 #344 is published.
• Define a bounded regular expression policy. PR Add Support for RN 0.71 #344 validates syntax, but it does not limit expensive patterns.

The fake rules engine is a permanent unit-test boundary. It is not an upstream compatibility shim.

Rules evaluations do not recover extraLogging. That field is deprecated and is not part of the new rules response.

User impact

There is no new user-visible behavior in this PR. Existing online and precomputed offline evaluation do not change.

Checks

• yarn tsc --noEmit -p packages/core/tsconfig.json
• Targeted ESLint for all changed TypeScript files
• 23 rules and wire tests
• 55 configuration tests
• 92 flags tests