Introduces new memory allocation functions, based on wled#4895 by @DedeHai
* keep a minimum of 15KB RAM available to UI - improves stability
* S3/S2/C3 automatically use "fast RTC Ram" for small data (reduces fragmentation)
* auto-detects PSRAM (or no PSRAM) when firmware was built with -D BOARD_HAS_PSRAM
* d_malloc() and d_calloc() prefer DRAM if possible (faster), but fall back to PSRAM when free RAM gets low.
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