Can cargo px run a command after a crate is built?

Nobody has claimed this yet.

Cargo still doesn't support something like [postbuild.rs](https://github.com/rust-lang/cargo/issues/545) which would run after the build (like `build.rs` runs before the build). The usual workaround is to build with another tool that first calls `cargo build`, then run the other command if the build is successful. Something like `make` or whatnot.

But, `cargo px` *is* another tool, one that was created explicitly to address shortcomings of Cargo. Could it maybe support this use case? (at least until Cargo has this feature natively).

Now, I had [another idea](https://github.com/rust-lang/cargo/issues/545#issuecomment-1502436045) to workaround this issue, which is basically to use the [xtask pattern](https://github.com/matklad/cargo-xtask) to drive the build (calling first `cargo build`, then the postbuild command). But I would like to avoid this if `cargo px` had a `postbuild` option.

Start by tracing cargo px's command entry point and how it invokes `cargo build`; compare the requested flow with the linked Cargo postbuild discussion and xtask pattern. Define how a postbuild command is configured and ensure it runs only after a successful build, then verify the behavior with the project's existing checks.

Written by the indexing model from the issue text.