Feature: Implement chromem as a single file

[hungrymonkey]

Chromem does not have built in support to save db as a single file. Instead, upstream offers the ability to save the db as a gob.

https://go.dev/blog/gob

https://github.com/philippgille/chromem-go/blob/main/persistence_test.go
https://pkg.go.dev/encoding/gob

With the gob, we package the vector db as a virtual filesystem and compress it with gz.

Options to consider

1. Do continue to support the directory vector db?
2. Do we compress all gob by default
3. Do we attempt to auto detect reading the archive?

[hungrymonkey]

https://github.com/philippgille/chromem-go/blob/main/persistence.go

I do not see random i/o, so it will be slow.