Preserve JSON-RPC error response ids

[jstar0]

Summary

Fixes #398.

Changes

• Preserve recoverable JSON-RPC request ids when request-envelope validation returns an Invalid Request error.
• Add regressions for an unsupported JSON-RPC version, a missing JSON-RPC version through handle_json, and a non-string method.
• Keep invalid request ids returning id: null.

Verification

bundle exec ruby -I lib -I test test/json_rpc_handler_test.rb
bundle exec ruby -I lib -I test test/mcp/server_test.rb test/mcp/server/transports/stdio_transport_test.rb test/mcp/server/transports/streamable_http_transport_test.rb
bundle exec rake test
bundle exec rake rubocop
bundle exec yard --no-output

[koic]

Since #400 has already been opened to address #398, I'm going to close this PR. Thank you.