Add features for wasm32-unknown-unknown target

[aspect]

Add new js feature that enables getrandom/js and uuid/js features (uuid already relays it to its own getrandom dependency) in order to be able to build moka for wasm32-unknown-unknown target (i.e. for in-browser execution using builders such as wasm-pack).

getrandom has platform-specific implementations for the random number generator and the crate requires an explicit selection of this feature for wasm32 target when the target OS is unknown, which is the case of the browser targets. If not specified, the build triggers the following error: https://github.com/rust-random/getrandom/blob/master/src/lib.rs#L244. This is just a feature relay that has no effect on the moka codebase.

[aspect]

Closing this PR - unable to build our project in release because getrandom is a dev-dependency where dev-dependencies can't be disabled from the crate that is dependent on moka and dev-dependency can not be made optional (cargo disallows). So in release mode, the added feature doesn't see the dev-dependency and errors out.

I will circle back once I am able to come up with the solution, as this seems to be a cargo issue (rust-lang/cargo#1596) in the meantime to advance on our project I am forced to work from the fork with dev-dependencies commented out.

I think it would be solvable by adding "testing" feature and migrating dev-dependencies under [target.'cfg(feature = "testing").dependencies], but not sure. In the meantime closing the PR to avoid this breaking anything.