bundle2.unbundlepart: keep an index of chunks and their locations In order to make unbundlepart seekable, we need to keep a record of where the chunks are so that we can go back to the correct point.

bundle2.unbundlepart: raise payloadchunks from a closure to a method In a future patch, seek() will need to make a new chunk iterator for the stream; this places it somewhere it can be called multiple times.

manifest: make lru size configurable On machines with lots of ram, it's beneficial to increase the lru size of the manifest cache. On a large repo, configuring the lru to be size 10 can shave a large rebase (~12 commits) down from 95s to 70s.