Completion refactors

[kmvanbrunt]

• Renamed Completions.completion_hint to hint.
• Renamed Completions.completion_error to error.
• Renamed Completions.completion_table to table and converted it from a string to a Rich Table.
• Removed DEFAULT_TABLE_HEADER.
• Renamed parser's table_header to table_columns.
• Renamed CompletionItem.table_row to table_data.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.51%. Comparing base (a89beaf) to head (688bba7).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1606      +/-   ##
==========================================
- Coverage   99.53%   99.51%   -0.03%     
==========================================
  Files          21       21              
  Lines        4746     4755       +9     
==========================================
+ Hits         4724     4732       +8     
- Misses         22       23       +1     

Flag	Coverage Δ
unittests	99.51% <100.00%> (-0.03%)	⬇️

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