Function diff_register_tool 

pub fn diff_register_tool(
    state: &impl McpStateView,
    sender: AccountId,
    intent: &McpIntent,
    timestamp: u64,
) -> Result<StateDiff, String>

Compute the StateDiff for RegisterMcpTool.

Creates the tool cell account with:

• Axiom bytecode as the implementation
• Schema hash, name, category stored in cell storage
• Commutative CALL_COUNT key registered so parallel invocations compose Updates McpRegistry storage to include the new tool.