Ship one preset cache per vendor in place of the profile JSONs

Each vendor's system presets serialize into a single <vendor>.opc built at
package time, and a shipped build carries that file alone — the profile JSON
and its sub-file tree are pruned. The vendor loader, the setup wizard's profile
list and the resource installer all read a vendor through its cache, falling
back to parsing whenever one is absent, stale or unreadable, so the cache stays
an optimization and never a source of truth. Caches hold presets in source form
and resolve inheritance at load, through the same code the JSON path uses.

tests/libslic3r/test_preset_bundle_loading.cpp

@@ -146,7 +146,7 @@ TEST_CASE("Current vendor type tolerates missing printer model", "[Preset][Bundl
 {
     PresetBundle bundle;
 
-    VendorProfile orca_vendor("ORCA");
+    VendorProfile orca_vendor; orca_vendor.id = "ORCA";
     VendorProfile::PrinterModel model;
     model.name = "Orca Test";
     orca_vendor.models.emplace_back(model);