eth_sendRawTransaction: expect -32602 for malformed-RLP decode failures

[manusw7]

What

Change the expected error code from -32000 to -32602 on the four eth_sendRawTransaction fixtures that submit undecodable payloads. Error messages are unchanged.

• integration/mainnet/eth_sendRawTransaction/test_01.json (truncated long-RLP tx)
• integration/mainnet/eth_sendRawTransaction/test_02.json (0xd4, truncated short-list)
• integration/mainnet/eth_sendRawTransaction/test_03.json (0xd4)
• integration/arb-sepolia/eth_sendRawTransaction/test_01.json (0xdeadbeef)

Why

A malformed/undecodable raw transaction is a parameter-decode failure, which per JSON-RPC 2.0 is -32602 (invalid params), not -32000. Clients currently diverge on the decode class; these PRs align it to -32602:

• internal/ethapi: return InvalidParams for malformed sendRawTransaction RLP ethereum/go-ethereum#35129
• rpc/jsonrpc: return InvalidParams for malformed sendRawTransaction RLP erigon#21701 (needs these fixtures to go green)
• eth_sendRawTransaction: RLP decode failure returns wrong JSON-RPC error code NethermindEth/nethermind#11921

Merge gates (why this is a draft)

1. Pending RPC Standards call confirmation (RPC Standards # 28, June 15, 2026, 15:00 UTC ethereum/pm#2120) that decode-failure on submit methods is -32602 and not a future catalog code.
2. Must not merge until internal/ethapi: return InvalidParams for malformed sendRawTransaction RLP ethereum/go-ethereum#35129 lands — until canonical geth emits -32602, flipping these shared fixtures turns the daily geth comparison runs red.
3. Pairs with rpc/jsonrpc: return InvalidParams for malformed sendRawTransaction RLP erigon#21701, which bumps RPC_VERSION to the tag cut here.

This PR's own CI will be red against geth for reason (2) — that's expected.