Restore code reverted by bad rebase

[cpuguy83]

b70e037 was originally based on a very old branch.
A rebase was required and was not properly reviewed. Many important changes were accidentially reverted as part of the commit.

This change brings those changes back.

[Copilot]

Pull request overview

This PR restores code that was accidentally reverted during a bad rebase of commit b70e0372. The changes primarily refactor a monolithic test into focused sub-tests, add new test coverage for gomod, cache management, and deb-specific features, and fix a missing DnfInstallWithConstraints option in RPM test dependency installation.

Changes:

• Refactors the large monolithic container test in test/linux_target_test.go into focused sub-tests (build_steps, sources, artifacts, tests, container), adds a testLinuxSpec helper to reduce boilerplate, adds testDepsOnly for deps-only target testing, adds extensive new test coverage for gomod replace directives, cache key management, deb-specific features (dpkg debug, upgrades, excludes config), and corrects multiple test targets from Container to Package where container-specific features aren't needed.
• Fixes targets/linux/rpm/distro/pkg.go by adding DnfInstallWithConstraints(opts) to test dependency installation and hoisting the progress group append before the closure.
• Removes the obsolete mariner2 entry from the artifact capabilities test targets map and adds a missing scanner.Err() check.

Reviewed changes

Copilot reviewed 1 out of 2 changed files in this pull request and generated no comments.

File	Description
test/linux_target_test.go	Major test refactoring: splits monolithic test into focused sub-tests, adds testLinuxSpec and testDepsOnly helpers, adds new gomod/cache/deb tests, corrects Container→Package targets, removes mariner2, adds scanner error check
targets/linux/rpm/distro/pkg.go	Adds DnfInstallWithConstraints(opts) to test dep install options, moves ProgressGroup append before the closure