feat(validation): align request/response validation and harden parsing/metrics behavior

[limehee]

Summary

This PR completes the validation/options overhaul for JSON-RPC request/response handling and aligns Spring auto-configuration with core behavior.

Key updates:

• Added symmetric request/response validation options in jsonrpc-core (ID rules, duplicate-member policies, field rejection policies).
• Added strict duplicate-member parsing support via shared payload reader and wired it through core/webmvc/autoconfigure.
• Exposed and bound response parser/validator options in Spring Boot auto-configuration.
• Fixed autoconfigure precedence so custom JsonRpcRequestValidationOptions / JsonRpcResponseValidationOptions beans are honored consistently.
• Added hard fail-fast constraints for invalid constructor/property inputs (including positive-only metric method-tag cap).
• Enforced hard cap semantics for metric method-tag cardinality under concurrency.
• Expanded tests across core/autoconfigure/webmvc/samples for success/failure/branch/concurrency paths.
• Updated docs and metadata (configuration reference, migration mapping, sample guides, expected JSON outputs).

Related Issues

• Closes [Feature] Symmetric request/response validation keys and response error.code policy expansion #20
• 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:

• Validation behavior is now more explicitly controlled through symmetric request/response options.
• Duplicate-member rejection can be enforced consistently for request/response raw parsing paths.
• Reserved method namespace (rpc.*) rejection and stricter fail-fast constraints are enforced where configured.
• Default behavior remains RFC-oriented and documented; strict toggles are opt-in via configuration.

Validation

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

Documentation

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