Improve emulation speed of large object allocations in Go

[Inphi]

Allocating large objects (i.e. > 32 KiB) takes a while under Cannon. On my machine (AMD Ryzen 7 3700X), it takes about 7 seconds to allocate a 32 MB byte slice (i.e. execute a single runtime.makeslice call). It takes roughly the same amount of time for even larger allocations.

This doesn't seem to slow down op-program execution too much. Probably because it doesn't create too many large objects. However, we should improve this aspect of emulation to avoid future surprises.