feat: implement context values

[Zaimwa9]

Closes #198

In this PR, we:

• Add EvaluationResult getEvaluationResult(EvaluationContext context) and remove all of the old engine APIs.
• Add support for JSONPath-enabled context values.
• Add evaluationContext/mappers for engine-API data interop
• Add script generate-engine-types to generate from flagsmith/sdk/evaluation-*-schema -> in pre-commit

Couple of questions concerning:

• hide_disabled_flags deprecation => ready to remove the commented code
• offlineHandler: It is wrapped between a wider getEnvironment that also includes getEnvironmentFromApi. I'm not seeing a huge value to migrate it but maybe I am missing something ? this would getEnvironmentFlagsFromDocument/getIdentityFlagsFromDocument -> getEnvironment -> this.offlineHandler.getEnvironment -> getEvaluationContext (using environment)
  Happy to change if misunderstood

    /**
     * Returns the current environment, fetching it from the API if needed.
     *
     * Calling this method concurrently while the environment is being fetched will not cause additional requests.
     */
    async getEnvironment(): Promise<EnvironmentModel> {
        if (this.offlineHandler) {
            return this.offlineHandler.getEnvironment();
        }
        if (this.environment) {
            return this.environment;
        }
        if (!this.environmentPromise) {
            this.environmentPromise = this.fetchEnvironment();
        }
        return this.environmentPromise;
    }

[Zaimwa9]

Added this manually to avoid relying on auto-generated redundant name keys:

export type Key1 = string;
/**
 * Key used for % split segmentation.
 */
export type Key2 = string;
/**

[Zaimwa9]

Question here about hidedisabled-flags. can remove

[khvn26]

Yup — I believe this is cleared up now; we don't use the setting for local evaluation mode.

[khvn26]

In general, the PR looks solid to me — just a handful of comments to address.

[khvn26]

Any way to avoid the type duplication here?

[Zaimwa9]

Yep, I created a joint model type at the root of evaluation folder. The idea being that:

• All types used in the code must come from this evaluation/models.ts
• If a type is needed from one generated file, it must be imported and re-exported from this entrypoint

[khvn26]

Yup — I believe this is cleared up now; we don't use the setting for local evaluation mode.