Improve specification of dynamic/static memory allocation

[Sword-Smith]

Cf. https://talk.neptune.cash/post/2/20, we should specify that about half of memory is available for static memory allocation $[2^{63}, 2^{64}-2^{32}]$ and half, $[2^{32}, 2^{63}-1]$ is available for dynamic allocation. Currently, we only specify how the kmalloc method words, and it only needs static memory from a region of size $2^{32}$.