add WITHOUT ROWID to all tables

[matt-codecov]

this has not made bulk inserts any faster, but it has reduced the resulting SQLite database size for my 110mb test report from 184mb to 105mb (notably, smaller than the input).

we may want to revisit this later when we do more reads

[matt-codecov]

whoops forgot i need to deal with SQLite not liking null local_span_id in the PK for context_assoc. i think i will just remove local_span_id from context_assoc and say, at least for now, that spans must link back to coverage samples somehow

[Swatinem]

lgtm, though as you mention, we should figure out what the write/merge/read numbers here are.