Implements `Result` in fast-calls. Note that the approach here is
slightly different. Rather than store the last result in the `OpState`,
we put it into the `OpCtx` which saves us a lookup and lock in the error
case. We do not have to lock this field as it's guaranteed only one
runtime and thread can ever access it.
The fastcall path for many ops can avoid doing a great deal of work,
even for `Result` return values. In the previous iteration of `ops`, all
`Result`-returning functions would fetch and lock the `OpState`,
regardless of whether it was used or not.
This is a new op system that will eventually replace `#[op]`.
Features
- More maintainable, generally less-coupled code
- More modern Rust proc-macro libraries
- Enforces correct `fast` labelling for fast ops, allowing for visual
scanning of fast ops
- Explicit marking of `#[string]`, `#[serde]` and `#[smi]` parameters.
This first version of op2 supports integer and Option<integer>
parameters only, and allows us to start working on converting ops and
adding features.
