Use Droppable Future instead of TaskMetadata

[coder137]

• TaskMetadata does not Drop when using tokio::select
• Added tokio integration tests for join! and select!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (07eda0e) to head (6cd106f).

Additional details and impacted files

@@            Coverage Diff            @@
##              main        #4   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         3    +1     
  Lines           65        64    -1     
=========================================
- Hits            65        64    -1     

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