Fix FixBigtableIO scalafix rule mangling named arguments

[kellen]

Summary

• The FixBigtableIO scalafix rule assumed rest args after (projectId, instanceId, tableId) were always positional, blindly wrapping index 0 with keyRanges = and index 1 with rowFilter =
• When the original code used a named argument like rowFilter = ... (skipping keyRanges), this produced invalid code: keyRanges = rowFilter = ...
• Fix checks if each arg is already a Term.Assign (named arg) and passes it through unchanged instead of wrapping it

Test plan

• Added test cases for all missing named-argument arities (4-arg named keyRanges, 4-arg named rowFilter, 5-arg both named, 5-arg mixed named/positional)
• All existing tests continue to pass
• sbt "tests-scio-0_152_12/test" passes

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.94%. Comparing base (2935047) to head (d8b539b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5948      +/-   ##
==========================================
- Coverage   61.94%   61.94%   -0.01%     
==========================================
  Files         323      323              
  Lines       11721    11721              
  Branches      818      818              
==========================================
- Hits         7261     7260       -1     
- Misses       4460     4461       +1     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.