Add support for importing objects

[LockedThread]

PR Description

Adds support for importing MVF geometry with kind object, such as desks, furniture, and fixtures.

Previously, object geometries were explicitly skipped during MVF parsing. This change preserves those features by extracting them into dedicated per-floor object layers, keeping them separate from spaces while making them visible and queryable in QGIS.

Changes

• Adds object geometry extraction in the MVF v3 parser.
• Creates per-floor object layers:
  • Objects for polygon objects
  • Object Lines for line objects
  • Object Points for point objects
• Adds object layer styling so imported furniture/fixture geometry is visually distinct from spaces, walls, doors, and windows.
• Includes object layers in the existing floor-group organization.
• Updates README documentation to mention object layer support.