Change attributes in RequestInfoImpl to be a ConcurrentHashMap

[jrduncans]

Fix a potential problem where an attribute added from one thread and then accessed afterwards from another thread may not be visible by using ConcurrentHashMap.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.37%. Comparing base (14167df) to head (1c81b69).
Report is 3 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #148      +/-   ##
============================================
- Coverage     92.39%   92.37%   -0.03%     
  Complexity     2515     2515              
============================================
  Files           167      167              
  Lines          7274     7274              
  Branches        986      986              
============================================
- Hits           6721     6719       -2     
  Misses          363      363              
- Partials        190      192       +2     

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