IteratableSplayTree: Add FindClosest()
boot loader: bios IA32: Add optional timestamps to debug output
boot loader: mount_file_systems(): Fix warning
boot loader: Optimize heap implementation

* Increase general allocation alignment from 4 to 8 byte. That was even
  incorrect.
* Use a splay tree instead of a singly linked list to manage the free
  chunks. That increases the size of the per-chunk structure to manage
  the free chunks, i.e. the of minimally allocatable memory size (from
  align(sizeof(void*)) to align(3 * sizeof(void*))), but make finding
  and inserting chunks much faster.

Fixes #10063 respectively improves the situation significantly.