require a store for buffering

[joshrwolf]

turns out the logs endpoint is:

1. different than the artifacts endpoint
2. doesn't support Range 😠

in light of that, add store as a required variable for the caller to create, seeing that it must properly be closed as well. this exposes the caller to httpreaderat which I don't love, but its simple to implement and seems worth it for easy conditional buffering

this also changes the return signature to a *zip.Reader, since it appears logs are also returned as zip files

[imjasonh]

Does httpreaderat just do buffering internally in this case? What do we get from it if we aren't using it to abstract Range?

[joshrwolf]

it conditionally buffers to memory (1Mb by default) and file (1Mb<x<1Gb)

[joshrwolf]

cc @jonjohnsonjr so this atrocity is on your radar. hoping to not need this soon