`gix::Repository` - make freelist controllable

The issue is that huge blobs can be read and right now, this memory would go back onto the free-list to never be released or shrunk. Right now, there are no limits.
Figure out a good API to deal with this - my idea would be to make it `take` able so settable so that it can be turned off, and taken, processed/shrunk, and then re-enabled by placing it back.