feat(src/internal/package2/pull.go): Check if package exists for OCI layers

[jamestexas]

Description

This PR's goal is to check if we have already have an OCI image locally before we pull it again. This should help ensure we don't re-pull each time. Tests will be done after the upcoming updates to publish are done.

This is the output comparing the execution time from a repeat run (removed other bits of the logging just to denote the pieces that mattered):

Output from the script:

First Run:

└> TIMEFMT=$'%*E total elapsed time\n%*U user CPU time\n%*S system CPU time'
time ./build/zarf-mac-apple package pull oci://ghcr.io/zarf-dev/packages/dos-games:1.1.0 --key=https://zarf.dev/cosign.pub -a arm64

5.109 total elapsed time
0.207 user CPU time
0.274 system CPU time

Repeat Run:

└> TIMEFMT=$'%*E total elapsed time\n%*U user CPU time\n%*S system CPU time'
time ./build/zarf-mac-apple package pull oci://ghcr.io/zarf-dev/packages/dos-games:1.1.0 --key=https://zarf.dev/cosign.pub -a arm64

0.866 total elapsed time
0.105 user CPU time
0.072 system CPU time

Related Issue

Fixes #2780

Relates to #

Checklist before merging

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

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