fix: resolve builtin variables in PackageInternal (prep, env)

[leodido]

Summary

Resolve builtin variables (${__pkg_version}, ${__git_commit}, ${__git_commit_short}) in PackageInternal fields (prep, env), not just in Config.

Part of https://linear.app/ona-team/issue/CLC-2147/fix-non-deterministic-version-across-packages

Problem

resolveBuiltinVariables() only resolved builtin variables in Config, but FindUnresolvedArguments() checks both PackageInternal and Config. This caused builtin variables in prep or env fields to be flagged as unresolved, failing the build with:

cannot build with unresolved argument "${__git_commit_short}": use -D__git_commit_short=value to set the argument

Example BUILD.yaml that would fail:

packages:
  - name: app
    type: yarn
    prep:
      - ["/bin/bash", "prepare.sh", "${__pkg_version}"]  # This was NOT resolved
    config:
      commands:
        build: ["./package.sh", "${__git_commit_short}"]  # This WAS resolved

Solution

Resolve builtin variables in PackageInternal before resolving in Config.

Testing

• Added TestResolveBuiltinVariablesInPackageInternal test
• All existing tests pass