Function record_span 

pub fn record_span(
    function_name: &str,
    level: Level,
    duration_us: u64,
    leases_held: usize,
    total_bytes: u64,
    nodes: usize,
    fbmu_writes: u64,
    fbmu_reads: u64,
    fbbu_writes: u64,
    fbbu_reads: u64,
    gpu_submits: u64,
    tasklet_submits: u64,
)

Record a completed instrumented span.

Called by the #[grafos_instrument] macro expansion at function exit. Formats the span data and emits it via the appropriate output channel.