Analyze task-like method signatures

[Jim8y]

Summary

• add an analyzer rule for task-like method return and parameter types
• report Task, Task, ValueTask, and ValueTask in non-async contract signatures
• register the new analyzer rule and cover it with unit tests

Validation

• dotnet test tests/Neo.SmartContract.Analyzer.UnitTests/Neo.SmartContract.Analyzer.UnitTests.csproj --filter "TaskLikeMethodSignature_ShouldReportDiagnostic" --no-restore
• dotnet test tests/Neo.SmartContract.Analyzer.UnitTests/Neo.SmartContract.Analyzer.UnitTests.csproj --no-restore

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.25%. Comparing base (512f278) to head (afe5579).

Additional details and impacted files

@@            Coverage Diff             @@
##           master-n3    #1588   +/-   ##
==========================================
  Coverage      80.25%   80.25%           
==========================================
  Files            295      295           
  Lines          25456    25456           
  Branches        3453     3453           
==========================================
  Hits           20429    20429           
  Misses          4132     4132           
  Partials         895      895           

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