Add RFC-aligned response protocol utilities to jsonrpc-core

[limehee]

Problem statement

jsonrpc-core currently provides first-class request-side protocol processing, but response-side protocol handling is not exposed as a dedicated core API.

To improve JSON-RPC 2.0 protocol completeness and consistency, the core should also provide standardized response envelope classification, parsing, and validation aligned with the specification.

Proposed solution

Add response-side protocol components to jsonrpc-core:

1. JsonRpcEnvelopeClassifier + JsonRpcEnvelopeType (REQUEST, RESPONSE, INVALID)

• Classify single and batch payloads into request/response/invalid at protocol level.

2. JsonRpcResponseParser

• Parse incoming JSON-RPC response payloads into a canonical incoming-response model.
• Preserve member-presence semantics (id present, result present, error present).

3. JsonRpcResponseValidator

• Enforce JSON-RPC 2.0 response constraints:
  • Top-level response must be an object.
  • jsonrpc MUST be "2.0".
  • id member MUST exist and MUST be string | number | null.
  • Exactly one of result or error MUST be present.
  • If error exists:
    • error MUST be an object.
    • error.code MUST be an integer.
    • error.message MUST be a string.
    • error.data remains optional.

4. JsonRpcResponseValidationOptions (fine-grained controls)

• Provide per-rule switches (Jackson-style configuration).
• Default values must follow RFC MUST constraints.
• RFC SHOULD / stricter operational rules (for example, rejecting fractional numeric IDs) are opt-in only.

5. Tests and docs

• Add unit tests covering success/failure/exception/branch scenarios for classifier/parser/validator.
• Update docs/protocol-and-compliance.md and docs/pure-java-guide.md with response-side handling and option usage.

Alternatives considered

• Keep current request-only scope:
  • Leaves response-side protocol handling unspecified in core.
• Add classifier only:
  • Insufficient for full response protocol correctness.

JSON-RPC behavior impact

No breaking change to existing request dispatch behavior.

This is an additive enhancement in jsonrpc-core to improve protocol completeness and RFC/spec alignment.

Additional context

Scope is strictly protocol-level and transport-agnostic.

No domain-specific policies (session registry, command/event mapping, tenant/edge rules, business status conversion) are included.