consider snmalloc as an alternative to mimalloc

[enihcam]

Since mimalloc has been unmaintained for a long while, I think it's probably time to add a build option to allow users choosing alternative memory allocator, e.g. snmalloc.

@rui314

[rui314]

Is mimalloc really unmaintained? The last release I can find at https://github.com/microsoft/mimalloc/tags is v2.1.2 which was released in April this year.

[enihcam]

there's no activities taken place after July 1st.

https://github.com/microsoft/mimalloc/activity

[rui314]

Three months are too short to consider the library unmaintained.

[Alcaro]

https://github.com/microsoft/mimalloc/graphs/code-frequency says wildly variable commit frequency is normal for this repo. microsoft/snmalloc#273 (comment) also says there's nothing to worry about.