Merge branch 'nnrw56-FOF_hashmap-patch-87425' of gitlab.cosma.dur.ac.uk:swift/swiftsim into nnrw56-FOF_hashmap-patch-87425

modify how we do allocs, i.e. keep a vector of pointers to arrays of chunks, instead of a linked list. this is messier, but at least the allocs are now even multiples of chunks. also fixed how chunk sizes are computed, chunks are now specified by their target size in bytes, currently a 4k memory page.

should benchmark some of the options at some point.

Merge branch 'nnrw56-FOF_hashmap-patch-87425' of gitlab.cosma.dur.ac.uk:swift/swiftsim into nnrw56-FOF_hashmap-patch-87425

 * Re-hash on overall and chunk fill rate,
 * Round table_size to nearest multiple of chunk size.

This will make changing them easier, should the need arise.

Several changes: a) store  the allocated chunks in `hashmap_alloc_t` blocks that are chained together and released block-wise, b) split `hashmap_get` into `hashmap_get` and `hashmap_lookup`, without the third parameter, c) bug fix, we were dropping chunks on recycling.

Next up: implement the iterator, try to make each chunk occupy a single memory page (usually 4kb).