[torchlib] Improve handling of SymInt[]

[justinchuby]

Previously sizes coming in as SymInt[] are first concatenated as INT64 then used. This created inefficiencies where we could not process any static dims from the size list and had to treat the whole shape as dynamic. In aten_expand, this meant we needed to add Abs on the shape.

This change updates the functions that take SymInt[] such that they are no longer turned into INT64 first. I updated aten_expand to process constant -1 values so an Abs is not required. I also added a helper merge_dims to create constants for consecutive constant dims first before concatinating.

[Copilot]

Pull Request Overview

This PR improves the handling of SymInt[] parameters in torch_lib operations by avoiding unnecessary conversion to INT64 tensors and enabling better optimization of static dimensions.

• Updates functions to accept Sequence[INT64] instead of IntType for shape parameters
• Introduces a merge_dims helper function to optimize consecutive constant dimensions
• Removes unnecessary Abs operations in aten_expand by handling constant -1 values directly

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
onnxscript/function_libs/torch_lib/ops/core.py	Updates multiple torch operations to use new shape handling approach and removes unnecessary type casting
onnxscript/function_libs/torch_lib/ops/common.py	Adds new merge_dims helper function to optimize consecutive constant dimensions

[codecov]

Codecov Report

❌ Patch coverage is 93.93939% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.98%. Comparing base (a925acc) to head (4334c37).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
onnxscript/function_libs/torch_lib/ops/core.py	91.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2522      +/-   ##
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+ Coverage   69.93%   69.98%   +0.04%     
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  Files         216      216              
  Lines       26052    26058       +6     
  Branches     2616     2618       +2     
==========================================
+ Hits        18219    18236      +17     
+ Misses       6931     6920      -11     
  Partials      902      902              

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