fix: optimize Excel row counting for files with abnormal max_row

[yuehong136]

What problem does this PR solve?

Some Excel files have abnormal max_row metadata (e.g., max_row=1,048,534 with only 300 actual data rows). This causes:

• row_number() returns incorrect count, creating 350+ tasks instead of 1
• list(ws.rows) iterates through millions of empty rows, causing system hang

This PR uses binary search to find the actual last row with data.

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• Performance Improvement

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 44.13%. Comparing base (1262533) to head (ebe2982).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main   #13018       +/-   ##
===========================================
+ Coverage   33.71%   44.13%   +10.41%     
===========================================
  Files          43       43               
  Lines        9378     9378               
  Branches      107      107               
===========================================
+ Hits         3162     4139      +977     
+ Misses       6207     5220      -987     
- Partials        9       19       +10     

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