Patches applied to vendored fast_matrix_market v1.7.6
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1. read_body_threads.hpp:158
   Cast discarded [[nodiscard]] return value to void.
   Fixes clang -Wunused-result warning (CRAN r-devel Fedora clang).
   Upstream: https://github.com/alugowski/fast_matrix_market/
   Applied: 2026-03-02
