Feature/radio select

[jeroenmoors]

Adds support for the Loxone Radio block ("type": "Radio") as a Home Assistant select entity (Platform.SELECT).

Changes:

• const.py: register Platform.SELECT in LOXONE_PLATFORMS
• select.py: new platform: LoxoneSelect discovers Radio controls, builds
  options from details.outputs (+ "All off" when allOff is present), tracks
  activeOutput state, sends output number via SENDDOMAIN; jLocked exposed
  as a read-only 'locked' attribute
• tests/test_select_mapping.py: unit tests for the pure build_option_maps
  helper (option building, all-off, duplicates, round-trip mapping)

Tested live on a Loxone Miniserver (v17.0.3.31) against HA (2026.6.4) with a
Radio block: entity appears correctly, reads activeOutput changes and sets outputs.

Please let me know if anything would not be inline with or up to expected standards!

[jmartasek]

Tested this on my setup (Loxone 17.1.6.30, HA 2026.7.1) - works well.

Thanks!

[JoDehli]

@jeroenmoors @jmartasek I merge it with the next release.