Add Mooncake frule and rrule implementations

[kshyatt]

Moving these over here to be more generic in response to comments on QuantumKitHub/TensorKit.jl#436

[codecov]

Codecov Report

❌ Patch coverage is 95.23810% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.07%. Comparing base (b4acb15) to head (c250dc0).
⚠️ Report is 25 commits behind head on main.

Files with missing lines	Patch %	Lines
ext/VectorInterfaceMooncakeExt.jl	95.23%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #36      +/-   ##
==========================================
+ Coverage   89.23%   93.07%   +3.84%     
==========================================
  Files           8       11       +3     
  Lines         325      491     +166     
==========================================
+ Hits          290      457     +167     
+ Misses         35       34       -1     

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[lkdvos]

Oh god, this is going to be a compat nightmare

[kshyatt]

I'm sorry 😭

[kshyatt]

Although is anyone using 1.6 anymore? We could just drop it in CI, the Project.toml just shows julia = 1...

[Jutho]

Two suggestions but otherwise approved.

[kshyatt]

Shouldn't we also take 1.6 out of CI, then?

[Jutho]

Shouldn't we also take 1.6 out of CI, then?

Fine by me.