Standardize imports by converting absolute imports to relative imports

[jrycw]

This PR aims to ensure consistency by converting all absolute imports to relative imports across most of our modules, as the majority already use relative imports. However, for the _data_color folder, I felt it was more natural to retain absolute imports, so those have been left unchanged.

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.70%. Comparing base (4771178) to head (8014ef0).
Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
great_tables/_utils.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #521      +/-   ##
==========================================
- Coverage   89.71%   89.70%   -0.01%     
==========================================
  Files          45       45              
  Lines        5202     5198       -4     
==========================================
- Hits         4667     4663       -4     
  Misses        535      535              

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[machow]

This LGTM