fix: improve api to get file slices splits

[xushiyan]

Description

Rename api split_file_slices() to get_file_slices_splits() and handle empty table case.

How are the changes test-covered

• N/A
• Automated tests (unit and/or integration tests)
• Manual tests
  • Details are described below

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.92%. Comparing base (bf5c6dd) to head (14219b9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #185      +/-   ##
==========================================
+ Coverage   90.81%   90.92%   +0.11%     
==========================================
  Files          20       20              
  Lines         958      959       +1     
==========================================
+ Hits          870      872       +2     
+ Misses         88       87       -1     

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