Arti fails to build on FreeBSD

On FreeBSD, cargo check --all-features fails with:

error[E0412]: cannot find type `RawNonZeroPid` in module `rustix::process`
  --> /root/.cargo/registry/src/index.crates.io-6f17d22bba15001f/secmem-proc-0.3.3/src/internals/prctl.rs:62:70
   |
62 | pub fn is_tracer_present() -> anyhow::Result<Option<rustix::process::RawNonZeroPid>> {
   |                                                                      ^^^^^^^^^^^^^ not found in `rustix::process`

    Checking tokio-socks v0.5.2
    Checking async-broadcast v0.7.1
For more information about this error, try `rustc --explain E0412`.
error: could not compile `secmem-proc` (lib) due to 1 previous error
warning: build failed, waiting for other jobs to finish...

• OS/Platform name and version: FreeBSD freebsd 14.1-RELEASE FreeBSD 14.1-RELEASE releng/14.1-n267679-10e31f0946d8 GENERIC amd64 (running under QEMU)
• Arti commit: 2a398f2a

This is because secmem-proc depends on rustix = 0.38, but uses RawNonZeroPid, which was removed in 0.38.0-alpha.1 (see also this commit).

secmem-proc needs to be updated to use NonZeroI32 instead of RawNonZeroPid.