refactor: Add a bin_unpack_bin_max for max-length arrays.

[iphydf]

These are statically allocated (e.g. uint8_t[1024]) arrays with variable length data inside them. Examples are group topics and nicknames.

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This change is 

[codecov]

Codecov Report

Attention: 26 lines in your changes are missing coverage. Please review.

Comparison is base (d0304d8) 74.47% compared to head (e337837) 74.51%.
Report is 1 commits behind head on master.

❗ Current head e337837 differs from pull request most recent head 58fac53. Consider uploading reports for the commit 58fac53 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2415      +/-   ##
==========================================
+ Coverage   74.47%   74.51%   +0.03%     
==========================================
  Files          87       87              
  Lines       26189    26211      +22     
==========================================
+ Hits        19505    19530      +25     
+ Misses       6684     6681       -3     

Files	Coverage Δ
toxcore/events/friend_connection_status.c	82.14% <100.00%> (ø)
toxcore/events/friend_message.c	81.73% <100.00%> (ø)
toxcore/events/friend_name.c	76.84% <100.00%> (ø)
toxcore/events/friend_status.c	81.92% <100.00%> (ø)
toxcore/events/friend_status_message.c	77.08% <100.00%> (ø)
toxcore/events/friend_typing.c	81.92% <100.00%> (ø)
toxcore/network.c	86.09% <100.00%> (ø)
toxcore/bin_unpack.c	78.43% <91.66%> (+1.01%)	⬆️
toxcore/events/conference_invite.c	14.42% <0.00%> (ø)
toxcore/events/conference_message.c	13.27% <0.00%> (ø)
... and 14 more

... and 7 files with indirect coverage changes

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[JFreegman]

Reviewed 27 of 27 files at r1, all commit messages.
Reviewable status: complete! 1 of 1 approvals obtained