feat: add Mappi32 board configuration and variant pinout

[riyanardian]

Description

This Pull Request adds official support and configuration for the Mappi32 development board (an ESP32-based board by KMTech).

Changes Included:

1. boards/mappi32.json: Added the main PlatformIO board definition files including core configs, upload speeds, and required build flags (-DARDUINO_ARCH_ESP32, -DVARIANT_MAPPI32).
2. variants/esp32/mappi32/: Added the specific variant directory containing:
   • variant.h: Defining the custom pin mapping for this specific hardware layout.
   • platformio.ini: Target configuration for environment testing.

Please review the implementation for merging into the develop branch. Thank you very much for your time and guidance! Best regards from Indonesia 🇮🇩🙏

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🤝 Attestations

• I have tested that my proposed changes behave as described.
• I have tested that my proposed changes do not cause any obvious regressions on the following devices:
  • Other (please specify below)
  • Tested specifically on the target Mappi32 hardware configuration via PlatformIO build verification.

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[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}