feat!: Context Values support, getEvaluationResult

[khvn26]

Contributes to #179.

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 EngineMappers class for engine-API data interop.
• Breaking change: EnvironmentModel class, used by IOfflineHandler, is no longer part of com.flagsmith.flagengine package. Methods carrying the engine business logic and sub-models/fields not relevant to the SDK are removed.
• Breaking change: drop Java 8 support.

[Copilot]

Pull Request Overview

This PR introduces support for context values and adds a new getEvaluationResult API while removing legacy engine APIs. The changes involve a breaking refactor from Java 8 to Java 11 and introduces JSONPath-enabled context value evaluation.

Key changes:

• Introduces EvaluationResult getEvaluationResult(EvaluationContext context) API replacing old model-based APIs
• Adds JSONPath support for context value evaluation and removes model-based segment evaluation
• Drops Java 8 support in favor of Java 11 minimum requirement

Reviewed Changes

Copilot reviewed 58 out of 58 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
pom.xml	Updates Java version from 8 to 11, adds JsonPath dependency and code generation plugin
src/main/java/com/flagsmith/flagengine/Engine.java	Replaces model-based feature evaluation with context-based evaluation using new API
src/main/java/com/flagsmith/flagengine/segments/SegmentEvaluator.java	Refactors from model-based to context-based segment evaluation with JSONPath support
src/main/java/com/flagsmith/mappers/EngineMappers.java	New mapper utility for converting JSON documents to engine contexts
src/main/java/com/flagsmith/interfaces/IOfflineHandler.java	Breaking change: replaces EnvironmentModel with EvaluationContext
src/test/java/com/flagsmith/flagengine/unit/segments/SegmentModelTest.java	Updates test to use new context-based evaluation instead of model-based

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[emyller]

Non blocking comments, since engine tests pass. These comments may or may not require attention.

P.S. Reviewing this on the iPad was frustratingly difficult, as is reading this Java codebase sometimes. I’m sorry for the somewhat poor review compared to my standards.

[Zaimwa9]

Looks good to me overall. I share Evandro's confusion surrounding boolean management - some clarification could help, also to have other implementations ISO.
I added a comment on the modulo evaluator

[Zaimwa9]

Loooks goooood. Approving but have minor comments / NIT so feel free to discard

[Zaimwa9]

Awesome 🥳

[matthewelwell]

Approving based on @emyller's review, and my subsequent follow up on the comments that he had left. I have not done a comprehensive review of the code, only the parts relevant to those conversations.