remove dependency on num_cpus

[jeremyandrews]

• remove external dependency on num_cpus(), use instead built-in available_parallelism() added in rust 1.59.0
• we originally listed requiring a much earlier version of Rust, but Goose wasn't correctly compiling with such an old Rust; bumping up our dependency to something more modern (also required by the time library used by one or more dependencies)
• closes remove dependency on num_cpus #542

[bebehei]

/ This might totally be unrelated, I'm new to the rust ecosystem /

I tried to build goose yesterday on NixOS and it already required rust version 1.65 because of the dependency on the time crate. See here:

bebe@gulasch:~/goose$ cargo build --example simple
    Updating crates.io index
  Downloaded rustls-pemfile v1.0.2
  Downloaded hyper-rustls v0.23.2
  Downloaded 2 crates (50.3 KB) in 0.77s
error: package `time v0.3.21` cannot be built because it requires rustc 1.65.0 or newer, while the currently active rustc version is 1.64.0

Wouldn't it be appropriate to even tag goose to have rustc version 1.65?

[jeremyandrews]

Yes, that's an excellent point!