Using arena for complex and long lived allocations?

So I am loading quite complex configuration where I don’t want to keep full configuration source loaded due to its size and lifetime (easily months or even years), so I need to copy some strings and construct some other non-u8 slices. I am using ArrayLists for creation these slices and their size is not easily determined in advance and later I do .toOwnedSlice. So during init/deinit of this structure I do tens of different allocations of same lifetime, so If I want to use gpa I have to keep tra...