Use mimalloc as default memory allocator on client

[TheRealMorgenfrue]

Fixes #160

[TheRealMorgenfrue]

Note that:

there is WASM support but it is not regularly tested. However, it should just work. > large allocations > 64MiB the memory is not returned because currently in WASM you can only grow memory. The best remedy at this point is to pre-reserve a large "mimalloc arena" from which mimalloc can allocate any block size (huge or small).

• Document WASM usage microsoft/mimalloc#308 (comment)

[TheRealMorgenfrue]

Cross-referencing this implementation with main might yield some insights into this.

[TheRealMorgenfrue]

In order to pre-reserve memory, a call to mi_reserve_os_memory is needed. However, by building from source, we don't have access to that function. Maybe configure the mimalloc rust wrapper for wasm instead of building from source.