Add support for zero-copy parsing

[zesterer]

Currently, only some initial experiments outside of the main codebase.

The new design departs quite a lot from master, to the point that it's likely to end up being a near-complete rewrite of the crate. However, benchmarks so far are promising!

These benchmarks have a few caveats:

• serde_json is not quite comparable because it's not performing zero-copy parsing: the final JsonValue contains String.
• pest is not quite comparable because it does not support parsing byte strings: it's parsing a version of the input that's been run through std::str::from_utf8

Regardless, the benchmark demonstrates well the substantial performance improvement over master (old chumsky has been included at the bottom as a point of comparison).

Along with support for zero-copy parsing, this new design also permits the following:

• A state type parameter, allowing mutable state to be passed down through the parser (useful for interning and more)
• A check-only mode that skips generating output
• Regex parsers

Unfortunately, the code requires GATs, a feature that is currently unstable (but might not be for much longer!).

• Reimplement all primitives
• Reimplement all combinators
• Reimplement error prioritisation
• Reimplement recovery
• Reimplement all text parsers
• Remove then_with
• Switch default behaviour of .parse(..) to .then_ignore(end()), add skip_all() combinator so the old behaviour can be opted into with .then_ignore(skip_all())

Closes #9

[oovm]

I want to experience this function but the following error is reported, how should I solve it?

error[E0309]: the parameter type `S` may not live long enough
   --> src\input.rs:233:64
    |
233 | ... E: Error<I::Token>, S, P: Parser<'a, I, E, S> + ?Sized>(parser: &P, inp: &mut InputRef<'a, '_, I, S>) -> PResult<Self, P::Output, E> {
    |                         -     ^^^^^^^^^^^^^^^^^^^ ...so that the type `S` will meet its required lifetime bounds...
    |                         |
    |                         help: consider adding an explicit lifetime bound...: `S: 'a`
    |
note: ...that is required by this bound
   --> src\input.rs:238:69
    |
238 | pub trait Parser<'a, I: Input + ?Sized, E: Error<I::Token> = (), S: 'a = ()> {
    |                                                                     ^^
error: missing required bound on `Iter`
   --> src\input.rs:402:5
    |
402 |     type Iter<'a>: Iterator<Item = T>;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |                                      |
    |                                      help: add the required where clause: `where Self: 'a`
    |
    = note: this bound is currently required to ensure that impls have maximum flexibility
    = note: we are soliciting feedback, see issue #87479 <https://github.com/rust-lang/rust/issues/87479> for more information

[zesterer]

@oovm Hey, I've just pushed up some fixes. It seems like I was working against an older nightly when developing this.

You can use cargo bench --features nightly to see the benchmark in action.

Obviously, please be aware that this is very early work, is missing a lot of combinators, and is likely going to be changing a lot before being merged. It's definitely not much more than an experiment right now, and I've only implemented the features required for the json benchmark to work.