fix(acp-client): normalize remote ACP proxy stdout

[wesbillman]

Summary

• normalize remote ACP proxy stdout before JSON-RPC framing
• sanitize control bytes and reassemble split JSON payloads safely
• add regression tests for chunked input, sanitization, and recovery paths

Should fix some of these:

[2026-02-23][20:17:22][agent_client_protocol::rpc][ERROR] failed to parse incoming message: expected value at line 1 column 1. Raw: ion checks"}]}}}

[2026-02-23][20:17:22][agent_client_protocol::rpc][ERROR] failed to parse incoming message: EOF while parsing a value at line 2 column 0. Raw: 

[2026-02-23][20:17:22][agent_client_protocol::rpc][ERROR] failed to parse incoming message: EOF while parsing a value at line 2 column 0. Raw: