Refactored hline and rect functions to be converted into labels

[LeoPrissberg]

This PR adjusts add_hline(), add_vrect(), and add_hrect() to convert annotations into labels. Similar to how add_vline() now converts to labels.

What’s included

Updated _process_multiple_axis_spanning_shapes()

• Hline now creates a single labeled shape (maps: right→end, left→start, middle→middle).

• Both vrect and hrect follow the same format for converting to labels.

  1. Remove "inside" and "outside" from annotation as it is not used for labels,
  2. Adds "middle" and "center" to labels if no other position is specified in the annotations

Skips creating a layout.annotation for all functions

Note: Tests needs to be changed to work with labels instead of annotations