refactor: modernize InspectorServer implementation

[bartlomieju]

Pulled out from #1198 this commit
modernizes InspectorServer implementation - it now relies more on tokio
than futures crate.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 99 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.65%. Comparing base (0c7f83e) to head (899830d).
⚠️ Report is 348 commits behind head on main.

Files with missing lines	Patch %	Lines
dcore/src/inspector_server.rs	0.00%	98 Missing ⚠️
dcore/src/main.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1207      +/-   ##
==========================================
- Coverage   81.43%   79.65%   -1.79%     
==========================================
  Files          97      100       +3     
  Lines       23877    25778    +1901     
==========================================
+ Hits        19445    20533    +1088     
- Misses       4432     5245     +813     

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[littledivy]

LGTM