* Improved heap and PSRAM handling
- Segment `allocateData()` uses more elaborate DRAM checking to reduce fragmentation and allow for larger setups to run on low heap
- Segment data allocation fails if minimum contiguous block size runs low to keep the UI working
- Increased `MAX_SEGMENT_DATA` to account for better segment data handling
- Memory allocation functions try to keep enough DRAM for segment data
- Added constant `PSRAM_THRESHOLD` to improve PSARM usage
- Increase MIN_HEAP_SIZE to reduce risk of breaking UI due to low memory for JSON response
- ESP32 makes use of IRAM (no 8bit access) for pixeluffers, freeing up to 50kB of RAM
- Fix to properly get available heap on all platforms: added function `getFreeHeapSize()`
- Bugfix for effects that divide by SEGLEN: don't run FX in service() if segment is not active
-Syntax fix in AR: calloc() uses (numelements, size) as arguments
* Added new functions for allocation and heap checking
- added `allocate_buffer()` function that can be used to allocate large buffers: takes parameters to set preferred ram location, including 32bit accessible RAM on ESP32. Returns null if heap runs low or switches to PSRAM
- getFreeHeapSize() and getContiguousFreeHeap() helper functions for all platforms to correctly report free useable heap
- updated some constants
- updated segment data allocation to free the data if it is large
- replaced "psramsafe" variable with it's #ifdef: BOARD_HAS_PSRAM and made accomodating changes
- added some compile-time checks to handle invalid env. definitions
- updated all allocation functions and some of the logic behind them
- added use of fast RTC-Memory where available
- increased MIN_HEAP_SIZE for all systems (improved stability in tests)
- updated memory calculation in web-UI to account for required segment buffer
- added UI alerts if buffer allocation fails
- made getUsedSegmentData() non-private (used in buffer alloc function)
- changed MAX_SEGMENT_DATA
- added more detailed memory log to DEBUG output
- added debug output to buffer alloc function
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