Overhaul memory allocation model

This commit makes several fundamental changes to memory handling:

- the frame allocator is now only an allocator for free frames, and does
  not track used frames.
- the frame allocator now stores its free list inside the free frames
  themselves, as a hybrid stack/span model.
  - This has the implication that all frames must currently fit within
    the offset area.
- kutil has a new allocator interface, which is the only allowed way for
  any code outside of src/kernel to allocate. Code under src/kernel
  _may_ use new/delete, but should prefer the allocator interface.
- the heap manager has become heap_allocator, which is merely an
  implementation of kutil::allocator which doles out sections of a given
  address range.
- the heap manager now only writes block headers when necessary,
  avoiding page faults until they're actually needed
- page_manager now has a page fault handler, which checks with the
  address_manager to see if the address is known, and provides a frame
  mapping if it is, allowing heap manager to work with its entire
  address size from the start. (Currently 32GiB.)

modules.yaml

@@ -22,6 +22,7 @@ modules:
             - src/kernel/debug.s
             - src/kernel/device_manager.cpp
             - src/kernel/font.cpp
+            - src/kernel/frame_allocator.cpp
             - src/kernel/fs/gpt.cpp
             - src/kernel/gdt.cpp
             - src/kernel/gdt.s
@@ -101,8 +102,7 @@ modules:
         source:
             - src/libraries/kutil/assert.cpp
             - src/libraries/kutil/bip_buffer.cpp
-            - src/libraries/kutil/frame_allocator.cpp
-            - src/libraries/kutil/heap_manager.cpp
+            - src/libraries/kutil/heap_allocator.cpp
             - src/libraries/kutil/logger.cpp
             - src/libraries/kutil/memory.cpp
             - src/libraries/kutil/printf.c
@@ -126,8 +126,7 @@ modules:
         source:
             - src/tests/address_manager.cpp
             - src/tests/constexpr_hash.cpp
-            - src/tests/frame_allocator.cpp
             - src/tests/linked_list.cpp
             - src/tests/logger.cpp
-            - src/tests/heap_manager.cpp
+            - src/tests/heap_allocator.cpp
             - src/tests/main.cpp