BUG: einsum with int8/uint8 input is buggy #24732

These tests are failing on macOS x86-64 and with clang-cl on Windows after the move to Meson:

FAILED core/tests/test_einsum.py::TestEinsum::test_einsum_sums_int8 - AssertionError:
FAILED core/tests/test_einsum.py::TestEinsum::test_einsum_sums_uint8 - AssertionError:

It passes with Clang on macOS arm64, and with MSVC on Windows. It's also passing with and without SIMD optimizations. So it's very likely to be a Clang + x86-64 + exact compile flags used bug in the C code somewhere. This needs investigation.