[oab24413gmai]

Summary:

• Add focused unit tests for edge cases in the JSON-RPC types: e.g., parsing of error objects with data payloads and missing/extra fields in ErrorObject, plus tests for Params covering empty params, by-name vs by-position parsing, and out-of-range index access via Params::sequence()/Params::parse(). Pure additive tests, no behavior change.
• Keep the change narrow so it is straightforward to review.

Notes:

• I kept this scoped to the relevant implementation and tests.