support on disk indices

[dleviminzi]

Adds support for storing faiss indices on disk.

Todo:

• [x] storage_type instead of on_disk
• [x] check for in-memory databases
• [x] skip the "create table xxx_index" code for disk indices

[asg017]

Quick update here: I intend to merge this, but found some errors while testing. The TL;DR is that the parse_constructor() function is quite buggy, mostly because I wrote it with raw string parsing, which isn't great.

So I'm writing a new tokenizer + parser for the parse_constuctor() function, which really cleans up the code, and will make it much easier to add new options in the future. Once I finish it, I'll probably merge this PR first, apply my changes, then make a new release this weekend

[dleviminzi]

Quick update here: I intend to merge this, but found some errors while testing. The TL;DR is that the parse_constructor() function is quite buggy, mostly because I wrote it with raw string parsing, which isn't great.

So I'm writing a new tokenizer + parser for the parse_constuctor() function, which really cleans up the code, and will make it much easier to add new options in the future. Once I finish it, I'll probably merge this PR first, apply my changes, then make a new release this weekend

Sounds good (I will add mmap option when new parser is in)

[asg017]

Merging into main, then will make some more edits + tests on top of that.

Let's move the discussion to #4