Add Heap class

[CptGibbon]

Add a Heap class to the heap inspection code, plus:

• Rename the existing Heap class to GlibcMemoryAllocator and the BaseHeap class to MemoryAllocator, which I think is more descriptive.
• Integrate the new Heap class into the heap command.

Hopefully this is the last heap-related class pwndbg needs for now, along with the recent Chunk, Arena & Bins classes.
This is a bare-bones implementation for now, just enough to for use in the heap command and there is some redundancy with existing classes & functions, which I plan to iron out in subsequent PRs. The end goal is to move most of the existing heap logic into the heap classes.

[codecov-commenter]

Codecov Report

Merging #1318 (505aa24) into dev (5a323b4) will decrease coverage by 0.16%.
The diff coverage is 18.18%.

@@            Coverage Diff             @@
##              dev    #1318      +/-   ##
==========================================
- Coverage   55.04%   54.87%   -0.17%     
==========================================
  Files         156      153       -3     
  Lines       19397    19387      -10     
  Branches     1804     1815      +11     
==========================================
- Hits        10677    10639      -38     
- Misses       8276     8298      +22     
- Partials      444      450       +6     

Impacted Files	Coverage Δ
pwndbg/commands/heap.py	77.98% <0.00%> (+0.44%)	⬆️
pwndbg/heap/ptmalloc.py	55.53% <16.66%> (-1.11%)	⬇️
pwndbg/heap/heap.py	54.54% <100.00%> (ø)
pwndbg/gdblib/config.py	68.88% <0.00%> (-10.53%)	⬇️
pwndbg/commands/vmmap.py	43.15% <0.00%> (-1.18%)	⬇️
pwndbg/lib/memory.py	93.15% <0.00%> (-0.28%)	⬇️
pwndbg/glibc.py	75.43% <0.00%> (ø)
pwndbg/disasm/arch.py	78.94% <0.00%> (ø)
pwndbg/color/memory.py	100.00% <0.00%> (ø)
... and 11 more

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[disconnect3d]

👍, we can merge it now though I'd love if we could include additional comments to the logic we have here ;p