Codegen: convert Arc<Box<T>> to Arc<T>

[Xynnn007]

This commit changes the generated ttrpc server from Arc<Box> to Arc. This helps the type conversion and also avoids extra runtime cost caused by double pointer.

Fixes #234

[Xynnn007]

@wllenyj sry please wait a moment. Let me test locally if sync version works fine with this.

[Xynnn007]

@wllenyj Add the line of sync version create_xxx_server

[Xynnn007]

Hi @wllenyj @Tim-Zhang What should I do else to move this forward?

[Tim-Zhang]

It will simplify the code:
before:

    let h = Box::new(HealthService {}) as Box<dyn health_ttrpc::Health + Send + Sync>;
    let h = Arc::new(h);
    let hservice = health_ttrpc::create_health(h);

after:

    let hservice = health_ttrpc::create_health(Arc::new(HealthService {}));

it also will cut down heap allocations, thanks @Xynnn007

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 24.74%. Comparing base (a9198f2) to head (444a490).
Report is 17 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #235      +/-   ##
==========================================
- Coverage   24.97%   24.74%   -0.23%     
==========================================
  Files          16       16              
  Lines        2651     2675      +24     
==========================================
  Hits          662      662              
- Misses       1989     2013      +24     

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