Rust rewrite of the server part of pmpm

Not quite feature-complete but already usable. Just cargo run (--release) it.

There's an experimental cmark feature flag. If enabled, pulldown-cmark is used instead of pandoc to split the markdown file into blocks. This should speed things up a lot for larger documents. You can try it with cargo run --features cmark (--release) or similar.

How much faster is this?

The end_to_end test contains a test case that gives a rough impression (but is not a proper benchmark!). The test sends a big .md file (~150KiB) to pmpm six times and outputs how long pmpm takes to process it. Before the third time, a small block in the .md file is modified. Before the sixth time, a large block in the .md file is modified.

Original python version

Running

$ RUST_LOG=end_to_end=debug cargo test --release --test end_to_end pythonbench

gives

Time from pipe send to websocket recv for initial: 1.83306244s
Time from pipe send to websocket recv for hot: 53.338903ms
Time from pipe send to websocket recv for hot: 425.407875ms
Time from pipe send to websocket recv for small block changed: 1.227729877s
Time from pipe send to websocket recv for previous hot: 427.112575ms
Time from pipe send to websocket recv for large block changed: 1.429425791s

I used python 3.10.

Rust version (without cmark feature)

Running

$ RUST_LOG=end_to_end=debug cargo test --release --test end_to_end naivebench

gives

Time from pipe send to websocket recv for initial: 1.526904827s
Time from pipe send to websocket recv for hot: 18.405244ms
Time from pipe send to websocket recv for hot: 15.999644ms
Time from pipe send to websocket recv for small block changed: 731.974341ms
Time from pipe send to websocket recv for previous hot: 13.48669ms
Time from pipe send to websocket recv for large block changed: 852.108441ms

I used rust 1.65.

Rust version (with cmark feature)

Running

$ RUST_LOG=end_to_end=debug cargo test --release --test end_to_end naivebench --features cmark

gives

Time from pipe send to websocket recv for initial: 1.315426906s
Time from pipe send to websocket recv for hot: 1.853992ms
Time from pipe send to websocket recv for hot: 1.549679ms
Time from pipe send to websocket recv for small block changed: 14.749363ms
Time from pipe send to websocket recv for previous hot: 1.982681ms
Time from pipe send to websocket recv for large block changed: 284.143211ms

I used rust 1.65.