Add runtime library dirs for run and test

[Sunrisepeak]

Summary

• Add [runtime] manifest metadata for package runtime library directories, dlopen libraries, and capabilities.
• Carry package runtime library directories through the build plan.
• Inject runtime library paths for mcpp run and mcpp test, so dlopen-based package closures can be exercised without wrapper scripts.
• Add manifest/unit coverage and an end-to-end dlopen fixture.

Test plan

• mcpp build
• mcpp test
• mcpp run -- --version
• MCPP=<rebased build output> bash tests/e2e/62_runtime_library_dirs.sh
• git diff --check