Fix upload pipeline for collection-instance (rigged) models; add validator dry-run

[Tweekazoid]

Fix upload pipeline for collection-instance (rigged) models; add validator dry-run

Problem

Models using collection-instance empties (e.g. rigged trams with body segments as instanced collections) were uploaded broken: geometry was missing, duplicated, or invisible because the pipeline only tracked direct parent/child hierarchies and didn't account for Blender's three-tier visibility system.

Changes

utils.py

• New get_hierarchy_with_instances() walks instance_collection references in addition to object.children, with cycle detection. Used by upload.py and autothumb.py.

upload.py

• Uses get_hierarchy_with_instances to build instance_collection_names and objects_in_instance_cols; excludes the latter from obnames to prevent double-loading.
• Added _snapshot_and_project_visibility / _restore_visibility helpers that project per-view-layer eye-hide state onto Object.hide_viewport / Collection.hide_viewport before save_as_mainfile(copy=True), then restore — so eye-hidden objects stay hidden after append into a fresh scene.

upload_bg.py

• After appending, discovers auto-loaded instance collections by walking the appended empties' instance_collection pointers instead of a second explicit libraries.load (which caused .001 duplicates).
• Body collections are unlinked from the scene collection so they don't render directly at origin, but remain in bpy.data so instance empties can still reference them for rendering.

upload_dryrun.py (new)

• Validator-only operator that runs the full upload-bg pipeline locally without a server round-trip.
• Mirrors prepare_asset_data logic, invokes upload_bg.py in a non-blocking subprocess thread, optionally opens the resulting blend in a new Blender instance.

ui_panels.py

• Dry-run button added to the upload panel, visible only to validators (profile_is_validator()), model/printable assets only.

[vilemduha]

This is a big deal if we finally fix it, we should have a call maybe.