multi-thread support

[alexspark]

from what i can tell, this library won’t give up the GVL during queries. i know very little about c extensions but i’m running sqlite in production with rails 7. but i would love to use this with active records’ load_async. but it’ll all be serialized reads unless the thread gives up the GVL.

[flavorjones]

I'm going to close this as a duplicate of #287 which has some background conversation about multi-thread support. Please drop a note there if you'd like!