Fix issue with parsing implied volumes

[tylerslaton]

This fixes two things:

• When we were evaluating the Dirs of a Container, we did not ensure a deterministic order. This would cause a flake in the calling tests where a behavior was wrong or right depending on the order of how the Dirs were evaluated. This is fixed by using typed.Sorted.
• If an existing Volume had "" set as the size, we would error and ignore it. This is a problem as some new logic allows for Volumes to be parsed and have "" as a size. The fix for this is to create a 0 size quantity when "" is set as the size.

I validate that this is gone by running the following script several times.

#!/bin/zsh
for i in {1..20}; do
  go test -count 1 -timeout 7m -run ^TestVolumes$ github.com/acorn-io/runtime/pkg/appdefinition &
done
wait

Checklist

• The title of this PR would make a good line in Acorn's Release Note's Changelog
• The title of this PR ends with a link to the main issue being address in parentheses, like: This is a title (#1216). Here's an example
• All relevant issues are referenced in the PR description. NOTE: don't use GitHub keywords that auto-close issues
• Commits follow contributing guidance
• Automated tests added to cover the changes. If tests couldn't be added, an explanation is provided in the Verification and Testing section
• Changes to user-facing functionality, API, CLI, and upgrade impacts are clearly called out in PR description
• PR has at least two approvals before merging (or a reasonable exception, like it's just a docs change)