feat: Autogenerate SPARSEMAT functions

[Copilot]

Description

Implements SPARSEMAT conversion to enable Stimulus autogeneration of sparse matrix functions. Functions with callbacks (igraph_eigen_matrix, igraph_eigen_matrix_symmetric) intentionally excluded per issue requirements.

Changes

C Converter Implementation

• Added Rz_SEXP_to_sparsemat() to convert R's dgCMatrix (column-compressed) to igraph's triplet format sparse matrix
• Extracts i/p/x/Dim slots from S4 object, iterates columns to populate entries

Interface Generation

• Removed IGNORE statements for igraph_sparse_adjacency, igraph_sparse_weighted_adjacency, igraph_weighted_sparsemat in tools/stimulus/functions-R.yaml
• Regenerated R/aaa-auto.R and src/rinterface.c via Stimulus

New Autogenerated Functions

1. sparse_adjacency_impl / sparse_weighted_adjacency_impl - graph from sparse adjacency matrix
2. weighted_sparsemat_impl - graph from weighted sparse matrix with edge attributes
3. get_laplacian_sparse_impl / get_adjacency_sparse_impl / get_stochastic_sparse_impl - sparse matrix extraction from graphs

Tests

• Added coverage for all 5 functions in test-aaa-auto.R

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• By submitting this pull request, I assign the copyright of my contribution to The igraph development team.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Autogenerate all SPARSEMAT functions</issue_title>
<issue_description>Need to implement SPARSEMAT conversion. If the functions use a callback, ignore for now.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Autogenerate all SPARSEMAT functions #2529

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[krlmlr]

Closing in favor of #2532.