feat: add indice and indice ranges mapping functions

[percevalw]

Description

• Add map_indices and make_indices_ranges with C++ backends and expose lengths.map_indices and lengths.make_indices_ranges with contiguous indice_dims, boundary handling, and flat indices with offsets and span ids for pooling with embedding_bag
• Introduce FoldedTensorLayout to store full_names and data_dims with named dimension resolution and helper methods and use it as the lengths container for FoldedTensor
• Improve as_folded_tensor to better infer dims and dtype from nested data and to accept named data_dims and better handle names and empty structures
• Benchmark script adds --cases to run selected cases and a new case for range based pooling and adjusts outputs

Checklist

• If this PR is a bug fix, the bug is documented in the test suite.
• Changes were documented in the changelog (pending section).
• If necessary, changes were made to the documentation.

[github-actions]

Coverage Report

Name	Stmts	Miss	∆ Miss	Cover
TOTAL	276	0	0	100.00%

1 file skipped due to complete coverage.

Coverage success: total of 100.00% is above 100.00% 🎉