* chore: adding unit tests for #366 and #326
* fix: duplicate submenu controls not generated for multiple installers
When multiple installers referenced the same expressions menu asset,
only one submenu control would be generated.
* fix: submenus incorrectly deduping across different postprocessing contexts
Fixes: #366, #326
* fix: postprocess context not being inherited into submenus (#326)
This caused issues where parameter mappings were not being applied to
submenus.
