storage: introduce a `revlog.reuse-external-delta` config This option goes a bit further and provides a way to get the same behavior as the `re-delta-all` optimisation from `hg debugupgraderepo`. The effect of the option is a bit hard to test as we do not have multiple diff algorithm at hand. However, we at least make sure the code path run.

     1

{

     2

    "conduit_uri": "https://phab.mercurial-scm.org/api",

     3

    "repository.callsign": "HG",

     4

    "arc.land.onto.default": "@",

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    "base": "hg:.^"

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}