Convert Quint empty tuples into uninterpreted types/values

[bugarela]

Hello

This is needed as a consequence of informalsystems/quint#1406, which started because we can't write empty records in TLA+ directly. In the end, we decided to use uninterpreted types/values to represent the unit type/value.

• Tests added for any new code
• Ran make fmt-fix (or had formatting run automatically on all files edited)
• Documentation added for any new functionality
• Entries added to ./unreleased/ for any new functionality

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.89%. Comparing base (8366559) to head (1cf2a58).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2869      +/-   ##
==========================================
- Coverage   78.91%   78.89%   -0.03%     
==========================================
  Files         467      467              
  Lines       15963    15966       +3     
  Branches     2589     2577      -12     
==========================================
- Hits        12597    12596       -1     
- Misses       3366     3370       +4     

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