Use camlzip package to implement a ZipStore.

[zoj613]

After recently reading the licensing terms camlzip, I realized that although it is licensed under LGPL, it contains a special exception that allows library authors to link to camlzip without being bound to the licensing terms of LGPL. The exception reads:

As a special exception to the GNU Lesser General Public License, you
may link, statically or dynamically, a "work that uses the Library" with
a publicly distributed version of the Library to produce an executable
file containing portions of the Library, and distribute that executable
file under terms of your choice, without any of the additional requirements
listed in clause 6 of the GNU Lesser General Public License.

I was initially not aware of this exception in the license and that drove the decision to implement ZipStore using zipc (which reads an entire zip archive into memory). This commit replaces zipc with camlzip and as a result re-works the ZipStore implementation.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.89%. Comparing base (22bd73a) to head (4079b74).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #90      +/-   ##
==========================================
+ Coverage   98.52%   98.89%   +0.37%     
==========================================
  Files          13       13              
  Lines        1555     1545      -10     
==========================================
- Hits         1532     1528       -4     
+ Misses         23       17       -6     

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