Add support for freebsd

[svenski123]

Building MystenLabs/sui which depends on this repo did not work on FreeBSD.

This PR corrects this.

[djc]

Maybe we can generalize to unix?

[svenski123]

Yeah that would be even better. I've swapped target_os for target_family.

[svenski123]

I've squashed the PR into one commit.

[svenski123]

msrv workflow failed due to an old rust version, I've updated the rust version to 1.81.0.

error: package `home v0.5.11` cannot be built because it requires rustc 1.81 or newer, while the currently active rustc version is 1.71.1
Either upgrade to rustc 1.81 or newer, or use
cargo update -p home@0.5.11 --precise ver
where `ver` is the latest version of `home` supporting rustc 1.71.1
Error: Process completed with exit code 101.

[djc]

I'm going to find another solution for that, but thanks for taking care of it. 😊

[djc]

If you can just remove the second commit, happy to merge this with the failing MSRV job.

[svenski123]

I've popped the msrv rust version commit.
Thanks for being so responsive and have a good weekend!