Try to use dmgs first on macos

[IanButterworth]

WIP, seems to work. Avoids the need for notarizing the stdlib.

Developed with Claude. I haven't reviewed the code closely yet.

% ./target/release/juliaup remove release && ./target/release/juliaup add release
    Deleting symlink julia-release.
      Tidyup Removed Julia 1.12.1+0.aarch64.apple.darwin14
      Remove Julia channel 'release' successfully removed.
    Checking for new Julia versions
  Installing Julia 1.12.1+0.aarch64.apple.darwin14
         Add Installed Julia channel 'release'
% ./target/release/julia +release -e "@time using Pkg"                           
  0.328271 seconds (517.75 k allocations: 34.026 MiB)

I had a previous attempt here #998

And some discussion here
JuliaLang/julia#54366
#1010

[DilumAluthge]

Might be worth sticking a link to this comment as a code comment somewhere here, otherwise people (like me) might forget why the setup-julia issue doesn't apply here.

[davidanthoff]

We should really handle that in the construction of the version db, right? I.e. where there is a dmg file available, the UrlPath path in the version DB should just point to that.

[IanButterworth]

I thought about that but would that be backwards compatible? The db needs to serve before and after we add dmg support

[davidanthoff]

The version db file itself is versioned, so when we update the schema (which this would essentially be a case of) we would publish it as version db 2 file, so any old client would just stay on the old version file. Would actually be good to test such a version db schema change with a relatively simply case like this one.