[cache] Optimize cache upload

[mikeland73]

Summary

This changes devbox cache upload so that it now longer has to build packages if they are already in cache.

For each package, it first checks if it is in target cache. If it is, it skips. Otherwise it builds/copies.

How was it tested?

[sentry-io[bot]]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ *exec.ExitError: <redacted usererr.combined>: nix path-info exit code: 1, output: <redacted []uint8>, err: <redac...** go.jetpack.io/devbox/internal/nix in StorePaths... View Issue
• ‼️ exec.ExitError: <redacted errors.withStack>: <redacted usererr.combined>: nix path-info exit code: 1, output: <... go.jetpack.io/devbox/internal/nix in StorePaths... View Issue
• ‼️ *exec.ExitError: <redacted usererr.combined>: nix path-info exit code: 1, output: <redacted []uint8>, err: <redac...** go.jetpack.io/devbox/internal/nix in StorePaths... View Issue
• ‼️ *exec.ExitError: <redacted usererr.combined>: nix path-info exit code: 1, output: <redacted []uint8>, err: <redac...** go.jetpack.io/devbox/internal/nix in StorePaths... View Issue
• ‼️ *exec.ExitError: error running script in Devbox: <redacted usererr.combined>: nix path-info exi...** go.jetpack.io/devbox/internal/nix in StorePaths... View Issue

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