cleanup(acounts_db): delete swissmap, disable fastloading

[Rexicon226]

Our swissmap implementation is just not faster than the Zig stdlib. It could make sense to have it if it did proper SIMD linear search for things like Pubkey keys, but it doesn't, which makes it consistently 40% slower. We rely on the SwissMap for its consistent layout, although the @Vector usage is currently plain illegal, so it doesn't make much sense to keep that either. On top of all of that, fastloading is broken anyways, loading real-world snapshots seems to fail bank field validation afterwards and it has some corrupt memory management leading to random segfaults.

All in all, deleting the swissmap and disabling fastloading (until we rewrite accountsdb to take a different approach, one that could be much easier/faster to fastload), seems like the easiest step forwards in terms of cleanup.

For now I've commented out the fastloading related code, perhaps it'll yield useful later.

[InKryption]

note: fastloading/saving is now deleted as of #929.