Trace single op.SplitToSequence

[titaiwangms]

This pull request updates several operator registrations in onnxscript/function_libs/torch_lib/ops/core.py to mark them as trace_only, which affects how these ops are handled during tracing and export. The most important changes are:

Operator registration updates (trace-only):

• Marked the aten::split and aten::split.Tensor operators as trace_only in the aten_split function registration.
• Marked the aten::split_with_sizes operator as trace_only in the aten_split_with_sizes function registration.
• Marked the aten::unsafe_split.Tensor operator as trace_only in the aten_unsafe_split function registration.

[gramalingam]

I am curious what motivated this. What does this change? Is there a unit test, if this is fixing a bug?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.42%. Comparing base (0d06d3b) to head (60f296b).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2817      +/-   ##
==========================================
+ Coverage   70.40%   70.42%   +0.01%     
==========================================
  Files         228      228              
  Lines       27140    27140              
  Branches     2727     2727              
==========================================
+ Hits        19108    19113       +5     
+ Misses       7096     7091       -5     
  Partials      936      936              

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