fix: isolate Travelpayouts cache keys by request variant (#3158)

* fix: isolate Travelpayouts cache keys by request variant

* test(aviation): lock Travelpayouts cache key variants

Pin v3/month-matrix/latest cache-key shapes so future refactors can't
silently regress to a single key per route. The month-matrix branch
intentionally keeps the v1 key — its upstream doesn't accept the
nonstopOnly/maxResults params, so filtering happens post-cache; the v3
and latest branches bake every upstream-varying option into the key.

End markers updated to step over the inner upstreamFailed-handling
else-block in each branch.

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Co-authored-by: Elie Habib <elie.habib@gmail.com>