fix(translator): ext-proc full duplex streamed trailers and validation

[guydc]

What type of PR is this?

What this PR does / why we need it: fix ext proc validation and trailer management for full duplex streamed mode

Which issue(s) this PR fixes:

Fixes #6270

Release Notes: Yes

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 70.73%. Comparing base (16747d4) to head (b1b6b5c). Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6323      +/-   ##
==========================================
- Coverage   70.76%   70.73%   -0.04%     
==========================================
  Files         220      220              
  Lines       37059    37069      +10     
==========================================
- Hits        26225    26220       -5     
- Misses       9299     9311      +12     
- Partials     1535     1538       +3     

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[arkodg]

/retest