Feature request: ability to install executables into a specific directory

[W1M0R]

I want to create my own virtual environment, but not using this method: https://docs.pkgx.sh/pkgx/pkgx#virtual-environments

Instead, I would like pkgx to gather all the selected packages and install them into a custom location, as a flat list of files. I would use this specifically for single-file executables.

I would imagine doing something like this: pkgx --install-dir "some-location" gum glow hx@123

An ls of some-location would produce:

> ls some-location
gum
glow
hx

I would then do:

export PATH=some-location:$PATH
gum --version
glow --version
hx --version

I would expect this method to download the tools to the regular pkgx cache location, and that install-dir would just copy (or link) the binaries to some-location. If I re-run the command, it should see that the binaries are already available in the cache, and then just re-copy/re-link them (if needed).

I wouldn't want the command to delete existing contents in some-location, but instead, it should append to some-location:

> ls some-location
(empty)
> pkgx --install-dir some-location gum
> ls some-location
gum
> pkgx --install-dir some-location glow
> ls some-location
gum
glow

Additional flags could be added that could request a recreate of some-location, instead of an append.

I wouldn't use this feature for packages that consist of multiple files, but if someone chooses to do so, I would expect the contents of that package to be copied into some-location.

I am already doing something like this manually using ubi, since a long Path environment variable on Windows becomes problematic. This is to overcome the following issue I am having with Mise: jdx/mise#5830

Seeing how the + syntax sets the Path (https://docs.pkgx.sh/appendix/faq#where-do-you-put-pkgs), it is clear that long fully-qualified locations are preferred by pkgx, which will surely cause similar issues on Windows as it does for Mise. Having the ability to copy the tools into some-location so that we can control our own Path, would be very helpful.

Similar functionality exists in aqua: https://aquaproj.github.io/docs/guides/build-container-image/#notes-of-aqua-cp