fix(spells): Allow parallel execution of immut service functions [NET-331]

[kmd-fl]

Tested: run 10 parallel spell.installs, and they worked fine, all spells were created quite fast.

[linear]

NET-331 Allow parallel execution of the same spell builtin function

Right now we take a lock before function execution, so the same function can't be executed simultaneously.

particle-builtin/src/builins.rs:149 :

    if let Some(function) = self
        .custom_services
        .read()
        .get(&args.service_id)
        .and_then(|fs| {
            fs.functions
                .get(&args.function_name)
                .or(fs.unhandled.as_ref())
        })
    {
        let mut function = function.lock();
        async_std::task::block_on(function(args, particle))
    } else {