feat: Go wasm

[markphelps]

This PR redoes the Go SDK to use pure WASM to get around the issues with Go and musl v glibc issues as mentioned in #719 and other issues/PRs

High Level Changes

1. Renamed flipt-engine-wasm to flipt-engine-wasm-js as it is JS specific since it uses wasm-bindgen to generate JS bindings
2. Created flipt-engine-wasm which compiles to 'pure' wasm using the wasm32-wasip1 target
3. Leverage wazero to handle the calls to / from wasm and Go without requiring CGo
4. Implement the fetching of flag state in pure Go as WASM cant do that yet, similar to how we do in the JS/browser SDKs
5. Changed some public facing API signatures for the Go SDK (see below as we need to decide if we want to do this now or not)

Go SDK API changes

⚠️ = breaking change

1. ⚠️ I changed WithUpdateInterval signature to use a time.Duration instead of int as its more idiomatic
2. I added the missing WithRef option
3. ⚠️ I changed the New func to take in a context.Context as wazero requires one, although we could undo this change and just use context.Background.. however using a context here will allow the user to set a timeout on the initial state fetch if they wish
4. ⚠️ I changed Close to also take in a context.Context for shutdown

TODO

• implement FetchMode, specifically support Streaming 😬
• Implement ErrorStrategy which means we'll need to capture the last error from fetch and hold it in the Go code
• Update READMEs / docs
• Benchmark against existing Go FFI based SDK
• pprof to check for memory leaks
• Decide what we want to do about potential breaking changes above. Either undo them or accept them and make this a new major version
• Probably need to implement retries for fetching like we do currently in the FFI engine
• Redo packaging for Go SDK (likely in another PR)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 321 lines in your changes missing coverage. Please review.

Project coverage is 80.07%. Comparing base (f81523e) to head (0ceb451).

Files with missing lines	Patch %	Lines
flipt-engine-wasm/src/lib.rs	0.00%	191 Missing ⚠️
flipt-engine-wasm-js/src/lib.rs	0.00%	115 Missing ⚠️
flipt-engine-ffi/src/lib.rs	0.00%	15 Missing ⚠️

Additional details and impacted files

@@                  Coverage Diff                  @@
##           static-musl-build     #744      +/-   ##
=====================================================
- Coverage              84.62%   80.07%   -4.56%     
=====================================================
  Files                      7        8       +1     
  Lines                   3922     4145     +223     
=====================================================
  Hits                    3319     3319              
- Misses                   603      826     +223     

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[markphelps]

I'm going to open this up for review as its already large enough. Will tackle the remaining issues in other PRs before release

[markphelps]

cc @jalaziz @piclemx this should finally fix the issues with have multiple versions of the Go SDK, allowing us to collapse it down to one that should work cross-platform

[jalaziz]

I'm so incredibly excited for this!!!! This will finally remove a fairly annoying road bump with our current usage of flipt <3

[markphelps]

@erka @GeorgeMac sorry for the massive PR!!

If you get a chance I would love some 👀 on evaluation.go as that is where the meat of the changes are and a bunch of concurrency stuff going on

[erka]

Overall it looks solid. I have only few comments about it.

[erka]

Probably there should be some reconnect logic. It will work fine to the first connection/timeout error and then client will not get any updates from Flipt (for example, the restart will kill all streaming for the clients). I don't know if I can emulate this with current open-source version. I just make a wild guess here.

[markphelps]

yeah you are right again! i was thinking of doing the retry/reconnect logic in another PR before release as this one is already quite large. I have it as a todo on the PR description though.