Welcome to better optimised op calls! Currently opSync is called with parameters of every type and count. This most definitely makes the call megamorphic. Additionally, it seems that spread params leads to V8 not being able to optimise the calls quite as well (apparently Fast Calls cannot be used with spread params).
Monomorphising op calls should lead to some improved performance. Now that unwrapping of sync ops results is done on Rust side, this is pretty simple:
```
opSync("op_foo", param1, param2);
// -> turns to
ops.op_foo(param1, param2);
```
This means sync op calls are now just directly calling the native binding function. When V8 Fast API Calls are enabled, this will enable those to be called on the optimised path.
Monomorphising async ops likely requires using callbacks and is left as an exercise to the reader.
- "SpawnOutput" extends "ChildStatus" instead of composing it
- "SpawnOutput::stdout", "SpawnOutput::stderr", "Child::stdin",
"Child::stdout" and "Child::stderr" are no longer optional, instead
made them getters that throw at runtime if that stream wasn't set
to "piped".
- Remove the complicated "<T extends SpawnOptions = SpawnOptions>"
which we currently need to give proper type hints for the availability of
these fields. Their typings for these would get increasingly complex
if it became dependent on more options (e.g. "SpawnOptions::pty"
which if set should make the stdio streams unavailable)
