feat: add response-side validation utilities and structured Spring validation config

[limehee]

Summary

This PR adds RFC-oriented protocol utilities and expands Spring Boot configurability, tests, and documentation.

Key updates:

• Added response-side protocol utilities in jsonrpc-core:
  • JsonRpcEnvelopeClassifier
  • JsonRpcResponseParser
  • JsonRpcResponseValidator
  • JsonRpcResponseValidationOptions
• Added configurable request params type-violation policy in core:
  • JsonRpcParamsTypeViolationCodePolicy
  • policy-aware DefaultJsonRpcRequestValidator
• Added structured Spring validation groups:
  • jsonrpc.validation.request.params-type-violation-code-policy
  • jsonrpc.validation.response.* (full response validation option surface)
• Added Spring auto-configured beans:
  • JsonRpcResponseValidationOptions
  • JsonRpcResponseValidator
• Added null-guard hardening in DefaultJsonRpcResponseValidator constructor.
• Expanded sample scenarios and integration coverage (Pure Java + Spring Boot).
• Updated README/docs/config metadata for implementation parity and IDE completion hints.

Related Issues

• Closes Add RFC-aligned response protocol utilities to jsonrpc-core #15
• Related #

Change Type

• Bug fix
• Feature
• Refactor
• Documentation
• Test
• Build/CI

JSON-RPC Impact

Describe protocol-level impact, if any:

• No protocol behavior change
• Request validation behavior changed
• Error mapping behavior changed
• Method registration/dispatch behavior changed

Details:

• Default runtime behavior remains RFC-aligned and backward-compatible unless new options are configured.
• New opt-in configuration controls request params type-violation mapping and incoming response validation strictness.
• Response-side utilities are additive and intended for client/bidirectional integration paths.

Validation

• ./gradlew test
• ./gradlew check
• Added/updated tests for new behavior

Documentation

• Updated README (if needed)
• Added migration notes for breaking changes (if any)