wasm support

[jameslahm]

currently, the spacebit_map and block_allocator are not compatible with wasm. We could implement a wasm feature, with specific spacebit_map and block_allocator enabled for it.

[playXE]

In what way gc/allocation.rs is not compatible with WASM I wonder? It does not seem to use mmap while spacebitmap and block_allocator do use it

[jameslahm]

just realize, it's my typo. 🤣