fix(lang-v2): honor bytemuckunsafe in declare_program! imports

[akash-osec]

Fixing finding AI # 28
declare_program! collapsed bytemuckunsafe into safe bytemuck, so imported unsafe zero-copy types were rejected unless they were already Pod and padding-free. Now this PR keep safe bytemuck checks for bytemuck, and for bytemuckunsafe emit unchecked Pod impls with v1’s packed default when repr is omitted.

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❌ Patch coverage is 93.75000% with 1 line in your changes missing coverage. Please review.
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Files with missing lines	Patch %	Lines
lang-v2/derive/src/lib.rs	93.75%	1 Missing ⚠️
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@@              Coverage Diff               @@
##             anchor-next    #4924   +/-   ##
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  Coverage               ?   64.65%           
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  Files                  ?      127           
  Lines                  ?    16618           
  Branches               ?        0           
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  Hits                   ?    10744           
  Misses                 ?     5874           
  Partials               ?        0           

Flag	Coverage Δ
v2	64.65% <93.75%> (?)

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[jamie-osec]

Can we document that this matches [Self::BytemuckUnsafe] as well? It's not obvious from the name, especially given is_bytemuck_unsafe is now added