updates `HEAP_SIZE` to be configurable for `embedded alloc` #159

Job	Run time
Build for all targets (app-radix-babylon, develop)	2m 35s
Build for all targets (app-kadena, develop)	2m 52s
Build for all targets (app-sui, develop)	2m 54s
Build for all targets (app-pocket, develop)	2m 55s
Build for all targets (app-starknet, develop)	3m 22s
Build for all targets (app-boilerplate-rust, main)	3m 29s
	18m 7s

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