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;
    }

[khvn26]

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

[khvn26]

We're close... just one comment from my side to resolve.

[khvn26]

LGTM