Make Serverside generic

[Kuhlwein]

Make serverside generic in order to support better type hinting.

Solves #272

[codecov-commenter]

Codecov Report

Merging #274 (1f42670) into master (2bf9f45) will increase coverage by 0.01%. The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##           master     #274      +/-   ##
==========================================
+ Coverage   84.12%   84.14%   +0.01%     
==========================================
  Files           9        9              
  Lines         945      946       +1     
==========================================
+ Hits          795      796       +1     
  Misses        150      150              

Impacted Files	Coverage Δ
dash_extensions/enrich.py	82.12% <100.00%> (+0.02%)	:arrow_up:

[emilhe]

Could you add a small example demonstrating how the new functionality is used?

[Kuhlwein]

Sure, you can use it as described on the related issue, for instance:

@callback(
    Output("some-output", "data"),
    Input("some-input", "value")
)
def foo(bar: str) -> Serverside[str]:
    return Serverside(bar)

It is of course still possible to omit the square brackets since Serverside defaults to Serverside[Any].

[emilhe]

I like this approach. One note is that in some cases, the return may not always be saved server side. But I guess in that case, one would just use a typehint of the form Union[str, Serverside[str]].