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Strip the versioner's prefixes with each instead of reduce (#2882)

`Versioner::Path#before` runs on every request of a versioned API and takes the
mount path and prefix off the front of PATH_INFO before looking for a version
segment:

    path_info = @prefixes.reduce(path_info) do |pi, path|
      pi.start_with?(path) ? pi.delete_prefix(path) : pi
    end

`@prefixes` holds at most two entries — a mount path and a prefix — and for an
API with neither it is empty. `Array` does not override `Enumerable#reduce`, so
that list pays the generic accumulator path on every request, which costs more
than the work it is driving.

`each` over the same list, assigning as it goes, is the same operation without
it. Measured in one process:

    one prefix    reduce 205 ns   ->   each  89 ns    2.31x
    no prefix     reduce 102 ns   ->   each  25 ns    4.02x

It allocates less too, which the timing alone does not show — 3 objects against
1 for identical work, the extra two being the Enumerable machinery rather than
anything the stripping needs:

    reduce  3.0 objects
    each    1.0 objects

End to end that is 166,376 -> 170,079 req/s on a small path-versioned API
(+2.2%, median of 9 runs interleaved with master's, Ruby 4.0.5 with YJIT), and
two fewer objects allocated per request. An API that declares no version never
builds this middleware and is untouched.

The result is byte-identical: the same prefixes are removed, in the same order,
under the same `start_with?` guard.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

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