Fix inner preparation behavior for Mooncake

[yebai]

See, chalk-lab/Mooncake.jl#878 (comment)

In the case of Mooncake, we're dealing with source transformation, so DI.PrepareInnerSimple() is more appropriate, good job for finding that.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 98.18%. Comparing base (45fad0e) to head (78895ed).

Files with missing lines	Patch %	Lines
...MooncakeExt/DifferentiationInterfaceMooncakeExt.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #948      +/-   ##
==========================================
- Coverage   98.19%   98.18%   -0.02%     
==========================================
  Files         133      133              
  Lines        7981     7982       +1     
==========================================
  Hits         7837     7837              
- Misses        144      145       +1     

Flag	Coverage Δ
DI	98.94% <0.00%> (-0.02%)	⬇️
DIT	96.19% <ø> (ø)

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