Close upstream utility parity coverage gaps

[jooh]

Summary

• cover upstream variable substitution utility cases for env aliases, workspace tokens, defaults, and devcontainerId behavior
• add deterministic Compose build-info parsing coverage for image/build shapes, defaults, targets, and build args
• add native Dockerfile utility coverage for final-stage naming, extraction, base image and USER resolution, ARG/ENV precedence, build arg expressions, syntax directives, quoted images, lowercase instructions, and ENV forms
• add Docker image-name qualification coverage while keeping live registry inspection out of scope
• update upstream test coverage map from Covered 9 / Partial 26 to Covered 12 / Partial 23

Tests

• make tests