Make count optional in MergeCells

[MaxDesiatov]

Attempt to fix some of the issues reported in #94.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@da9a091). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #119   +/-   ##
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  Coverage        ?   97.34%           
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  Files           ?        8           
  Lines           ?      301           
  Branches        ?        0           
=======================================
  Hits            ?      293           
  Misses          ?        8           
  Partials        ?        0           

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