[x] http: avoid buffering header
This changes the buffernig logic for headers as to not unnecessarily create buffer queue entries when no buffering is required. Also removes the need to perform object allocations while buffering.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines