Better --verbose flag descriptions for *bins commands

[CptGibbon]

Update the help fields of the *bins commands' --verbose argument to better reflect what it does.

e.g. "Show all fastbins, including empty ones", rather than simply "Show extra detail".

Resolves #1664

[codecov-commenter]

Codecov Report

Merging #1665 (ac7b670) into dev (ca5e6f5) will not change coverage.
The diff coverage is 100.00%.

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@@           Coverage Diff           @@
##              dev    #1665   +/-   ##
=======================================
  Coverage   59.20%   59.20%           
=======================================
  Files         173      173           
  Lines       20933    20933           
  Branches     1839     1839           
=======================================
  Hits        12394    12394           
  Misses       7943     7943           
  Partials      596      596           

Impacted Files	Coverage Δ
pwndbg/commands/heap.py	74.32% <100.00%> (ø)

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