feat(rig-sqlite): impl InsertDocuments trait for sqlite

[howenyap]

Changes

• implements InsertDocuments trait for rig-sqlite, part of feat: impl InsertDocuments for all vector store providers #565
• updated documentation comments to use insert_documents
• updated outdated top_n call here
• added integration test to cover insert_documents
• updated sqlite connection to be in memory only, there are only two tests now but this would make tests less flaky in the future, in case we have leftover rows from previous runs (lmk if i should remove this)

[howenyap]

hm errors are unrelated to my changes, all pointing towards the gemini client

saw some changes to client in the main branch so i rebased, not sure if it'll fix the errors

[howenyap]

verified that previously failing actions now pass locally