Add Legic Prime 7-slot RDV4 standalone mode (HF_LEGIC_RDV4)

[digitalhoax]

Problem:
The existing Legic standalone mode (HF_LEGIC) supports only a single tag slot in RAM/flash with basic controls. Users on the Proxmark3 RDV4 require multiple persistent memory slots with clear LED state feedback for field use.

Change:

• Implemented armsrc/Standalone/hf_legic_rdv4.c providing 7 independent Legic Prime tag slots.
• Added SPIFFS persistence (hf-legic-slot-1.bin - hf-legic-slot-7.bin).
• Implemented binary LED slot signaling using LEDs B, C, and D.
• Added single click (slot cycling), double click (scan/emulate toggle), and long hold (exit) with debounced button release detection.
• Synchronized build definitions in Makefile.hal, Makefile.inc, StandAloneOption.cmake, and StandAloneSource.cmake.

Behaviour change:

• New standalone mode option STANDALONE=HF_LEGIC_RDV4 available for RDV4 targets.
  Testing:
• Built warning-free on PM3RDV4 ARM toolchain (gcc 13.3).
• Verified warning-free host client compilation on macOS (clang).
• Tested on RDV4 hardware: slot cycling (1-7), scan-to-emulate auto-transition, double-click toggling, and flash memory persistence across power cycles.

[github-actions]

You are welcome to add an entry to the CHANGELOG.md as well

[digitalhoax]

Full disclosure: this is AI assisted code (Gemini 3.7 Flash). All checks in PR performed manually and on device.