feat(wasm): add beerus-web wasm library

[sergey-melnychuk]

This PR brings proper WebAssembly support to Beerus.

The demo web page is added in order to showcase expected usage.

Reference:

• [WIP] feat(wasm): beerus demo page #691
• https://github.com/sergey-melnychuk/helios/commits/beerus-wasm/
• https://github.com/sergey-melnychuk/sequencer/commits/beerus-wasm/
• https://github.com/sergey-melnychuk/cairo-vm/commits/beerus-wasm/
• https://github.com/sergey-melnychuk/cairo/commits/beerus-wasm/
• deps: upgrade blockifier-related dependencies #754

Closes #692
Closes #674

[sergey-melnychuk]

Current problem is that blocking IO must be called from single-threaded JS runtime, which in practice is impossible.

There are two strategies:

• a major refactoring of blockifier + cairo-vm + cairo-lang-* crates, which is already in progress. Next step in this direction is a significant hint executor refactoring (avoid shared mutable state)
• using tools like asyncify to hack into the wasm runtime internals and do manual stack unwinding in async calls, in order to make them behave like non-async ones.

I am currently pursuing both approaches simultaneously to investigate the best way to proceed, but just one of them to work should be enough.

[sergey-melnychuk]

At this point the blocking IO is no longer an issue - the easiest way to make it work was to run beerus in a web worker, and inject blocking http call through JavaScript function.

Currently the problem is with parsing Sierra program from Felt252: the root cause is that size_of<usize> is 4 (bytes) in wasm runtime (as opposed to 8 in x86_64), thus trying to parse a usize from u64 fails.

Some extra juggling with dependencies and features was necessary to ensure that the same codebase can compile to both x86_64 and wasm32 target architecture. See commits in beerus-wasm in sequencer, cairo-vm and cairo repositories (links in a PR description).

[sergey-melnychuk]

[sergey-melnychuk]

The PR is ready for review. @LKozlowski @ICavlek PTAL.

[ICavlek]

I have added couple of comments, but in general excellent job :) I have managed to run it from my side and I had no issues :)

[ICavlek]

LGTM, please also check the package-lock.json, license value

[LKozlowski]

I went through the PR commit by commit and got the general idea behind that PR. It's a huge PR and as you said there are still a lot of rough edges that need to be polished in the future, but as for the general it seems very easy to follow. I haven't found anything particularly odd that needs to be fixed now. I mostly checked the rust code and skimmed through JS, as I assume this is just for demo purposes for now and will be heavily changed in the future. I think we should merge it as soon as possible and set up a job that will test the wasm code regularly.
The most important thing is that it is working, and the details of it can be ironed out very easily.