fix double serialize on invoke

[LucasJavaudin]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• New Binding issue #___
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes, and the changes were approved in issue #___
• No

Checklist

• When resolving issues, they are referenced in the PR's title (e.g fix: remove a typo, closes #___, #___)
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.
• I have added a convincing reason for adding this feature, if necessary

Other information

When using the invoke function asynchronously to run a Rust function and return a value that can be serialized, the serialized value is serialized a second time, uselessly. This is because of a useless conversion in the function hooks::respond_async_serialized: The task returns a Result<JsonValue, InvokeError> that is converted into a InvokeResponse by the call to into(). An InvokeResponse is in practise exactly equal to a Result<JsonValue, InvokeError> so the conversion should be immediate. However, the call to into() use the impl From<Result<T, InvokeError>> for InvokeResponse (where T: Serialize), which serialize the JsonValue into a JsonValue (and that is not instantaneous).

[lucasfernog]

Nice catch, thanks!