Refactor TraceState for fewer allocations #238
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Currently
TraceStateis aVecDequebecause the spec has inserts moving the associated key to the front of the list. This is unfortunate asVecDequewill always allocate (see rust-lang/rust#68990).This change addresses the issue by instead having
TraceStatestore anOption<VecDeque<_>>, allowing the common case where there is no tracestate content to not heap allocate.