Move encrypted DNS state to crate shared between iOS and everyeone else

[MarkusPettersson98]

Move the Encrypted DNS config selection algorithm to the mullvad-encrypted-dns-proxy crate where both mullvad-ios and mullvad-daemon can consume it.

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This change is 

[linear]

DES-1320 Move config selection algorithm out of `mullvad-ios`

[MarkusPettersson98]

Maybe it makes more sense to name the state module cache instead? 🤔

[dlon]

Reviewed 3 of 3 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @MarkusPettersson98)

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mullvad-encrypted-dns-proxy/src/state.rs line 34 at r1 (raw file):

    /// Select a config.
    /// Always select an obfuscated configuration, if there are any left untried. If no obfuscated
    /// configurations exist, try plain configurations. The order is randomized due to the hash set

Nit: The fact that hash sets are used sounds like an implementation detail. Maybe it should not be mentioned here.

[dlon]

Maybe it makes more sense to name the state module cache instead? 🤔

Not to bikeshed, but I guess that this module has two responsibilities: (1) owning a cache, (2) keeping track of used configs. Maybe "state" is vague enough to encompass both?

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @MarkusPettersson98)

[MarkusPettersson98]

Fair enough, point 2 would make 'cache' misleading.

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @dlon)

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mullvad-encrypted-dns-proxy/src/state.rs line 34 at r1 (raw file):

Previously, dlon (David Lönnhager) wrote…

Nit: The fact that hash sets are used sounds like an implementation detail. Maybe it should not be mentioned here.

I agree that it an implementation detail, but this is something we would like to change eventually. Making it as visible as possible might make us consider changing it sooner rather than later 🤷 ?