[Bug]: JSONRPC error mapping #413

What happened?

Running the @a2a-project/a2a-tck I got a few discrepancy on JSONRPC error mapping compared to JSONRPC 2.0 spec

Analysis of the issues:

1. Test case 0 - Missing jsonrpc field:
   - TCK expects: -32600 (Invalid Request) ✅ CORRECT
   - SUT returns: -32602 (Invalid params) ❌ INCORRECT
   - Verdict: SUT is wrong - missing jsonrpc makes the request invalid per JSON-RPC spec
2. Test case 3 - Invalid id type:
   - TCK expects: -32600 (Invalid Request) ✅ CORRECT
   - SUT returns: 500 HTTP error ❌ MAJOR BUG
   - Verdict: SUT is wrong - it should return -32600, not crash with 500
3. Test case 4 - Invalid params type:
   - TCK expects: -32602 (Invalid params) ✅ CORRECT
   - SUT returns: -32600 (Invalid Request) ❌ INCORRECT
   - Verdict: SUT is wrong - when params is wrong type, it's invalid params, not invalid request

Relevant log output

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