fix(emulator): correct heap_size calculation in LinearMemoryLayout::tracked_ram_size

[kurahin]

Previously, heap_size was computed as heap - heap_start, which always evaluated to zero because heap_start returns the same field. This caused tracked_ram_size to undercount RAM-checked addresses by entirely omitting the heap. The calculation now uses heap_end() - heap_start(), which reflects the actual heap span between the heap base and the stack bottom

[github-actions]

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[kurahin]

I have read the CLA Document and I hereby sign the CLA

[sjudson]

Excellent catch, this definitely would be a problem.