Removal of resolution context in wrapper.invoke

[nerfZael]

The goal of this PR is to make the wrapper trait, specifically the invoke method, not coupled with the resolution context.
Resolution context passing has already been achieved through the subinvoker construct (This part was implemented in a previous PR: #94). Which means the resolution context argument is now obsolete.

Additionally, the invoke_wrapper method signature has been changed to:

 fn invoke_wrapper_raw(
    &self,
+   wrapper: &dyn Wrapper,
    uri: &Uri,
    method: &str,
    args: Option<&[u8]>,
    env: Option<&Env>,
    resolution_context: Option<&mut UriResolutionContext>,
) -> Result<Vec<u8>, Error>;

The wrapper argument has been made a reference since there was no need to keep it as Arc after the subinvoker implementation (which is an Arc itself).

Less notable changes:

• Both invoke_wrapper and invoke_raw in the PolywrapClient now use invoke_wrapper_raw under the hood.