feat: use builtin ORAS cache for skeleton packages

[AustinAbro321]

Description

In #3767 we created a generic cache for ORAS layers. This is used by default, but we also have a special implementation of caching specifically for skeleton packages. This PR removes that implementation so only the generic cache is used.

Checklist before merging

• Test, docs, adr added or updated as needed
• Contributor Guide Steps followed

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[codecov]

Codecov Report

Attention: Patch coverage is 7.14286% with 13 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/internal/packager2/layout/import.go	7.69%	12 Missing ⚠️
src/pkg/zoci/common.go	0.00%	1 Missing ⚠️

Files with missing lines	Coverage Δ
src/pkg/packager/pull.go	0.00% <ø> (ø)
src/pkg/zoci/common.go	0.00% <0.00%> (ø)
src/internal/packager2/layout/import.go	49.87% <7.69%> (+0.12%)	⬆️

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