… 2.31)

minimap2 2.31 dropped the bundled `lib/simde` submodule (it now ships only a
standalone Makefile.simde and expects the consumer to provide simde), so the
`simde` feature's `cc.include("minimap2/lib/simde")` pointed at a path that no
longer exists, failing with:

    minimap2/ksw2_ll_sse.c:7:10: fatal error: simde/x86/sse2.h: No such file or directory

Add simde as a minimap2-sys submodule (simd-everywhere/simde, pinned to v0.8.2)
and include it from build.rs instead. Exclude its test/ dir from the published
package (mirrors the old /minimap2/lib/simde/test exclude); packaged size stays
~1 MiB compressed. Verified `cargo test --features simde` passes for both
minimap2-sys and the top-level minimap2 crate.