pub fn set_block_diff(&self, block_diff: u32) {
        let cell = self.inner.get_or_default();
        if let Some(metadata) = &mut *cell.borrow_mut() {
            metadata.block_diff = Some(block_diff);
        }
    }
Sets the difference between the latest sealed L2 block and the requested L2 block for the current JSON-RPC method call.
It will be used as a metric label for method latency etc.

This should be called inside JSON-RPC method handlers; otherwise, this method is a no-op.
core/node/api_server/src/web3/backend_jsonrpsee/metadata.rs