Function phytrace_agent_create_mock 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn phytrace_agent_create_mock(
    source_id: *const c_char,
    source_type: i32,
) -> *mut PhyTraceAgentHandle

Create a PhyTrace agent with a mock transport for testing.

This is a convenience function that creates an agent configured with a MockTransport — useful for unit tests and integration tests where no real PhyCloud endpoint is needed.

source_id — Null-terminated source identifier string. source_type — Integer source type constant (e.g., PHYTRACE_SOURCE_TYPE_AMR).

Returns a heap-allocated agent handle on success, or null on failure.