fix(mcp): keep tool errors out of server breaker

[Muhtasham]

Problem

Repeated CallToolResult.isError responses currently increment the server-wide MCP circuit breaker. Invalid arguments or missing resources can therefore block neighboring valid tools even though every RPC proved the transport healthy.

Fix

Reset server-health breaker state after every completed MCP RPC. Tool-level errors remain unchanged and visible to the caller; transport/session exceptions continue to drive the breaker.

Verification

• Reproduced on current main: the fourth application rejection was replaced by a server-unreachable error
• Added an invariant test proving repeated application errors remain visible without opening the breaker
• scripts/run_tests.sh tests/tools/test_mcp_circuit_breaker.py tests/tools/test_mcp_tool.py tests/tools/test_mcp_tool_session_expired.py -q — 111 passed
• Ruff check — passed
• git diff --check — passed

[alt-glitch]

This was generated by AI during triage.

Duplicate of #74045. It implements the same completed-RPC breaker reset, while #74045 additionally covers the auth and session-recovery paths.