Use Send-less BoxFuture for HttpClient Service impl on wasm

[jplatte]

The dependencies required for the experimental-oidc feature don't currently compile on WASM, but once they do this is another thing inside this repo that's required for the feature to work on WASM.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.40%. Comparing base (2bd8c56) to head (1cfa087).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4544   +/-   ##
=======================================
  Coverage   85.40%   85.40%           
=======================================
  Files         285      285           
  Lines       32213    32213           
=======================================
+ Hits        27511    27512    +1     
+ Misses       4702     4701    -1     

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