add: FOC_DEVNET_BASEDIR support for overriding ~/.foc-devnet

[redpanda-f]

Configurable Base Directory with FOC_DEVNET_BASEDIR

Adds support for the FOC_DEVNET_BASEDIR environment variable to override the default ~/.foc-devnet base directory. The variable supports tilde expansion for paths like ~/custom-foc-devnet. Falls back to the default when the variable is not set. Includes the shellexpand crate for robust path expansion.

[redpanda-f]

split off from #40 so that CI issues can be tackled separately

[Copilot]

Pull request overview

This PR adds support for configuring the base directory of foc-devnet through an environment variable FOC_DEVNET_BASEDIR, allowing users to override the default ~/.foc-devnet location. The implementation uses the shellexpand crate to handle tilde expansion in custom paths.

Changes:

• Modified foc_devnet_home() function to check for FOC_DEVNET_BASEDIR environment variable before falling back to default
• Added shellexpand dependency for tilde expansion support in custom paths
• Updated function documentation to reflect new environment variable behavior

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/paths.rs	Modified foc_devnet_home() to check FOC_DEVNET_BASEDIR env var and apply tilde expansion before defaulting to ~/.foc-devnet
Cargo.toml	Added shellexpand = "3.0" dependency for tilde expansion functionality
Cargo.lock	Added shellexpand 3.1.1 lockfile entry with its dependency on dirs crate

[Copilot]

@redpanda-f I've opened a new pull request, #53, to work on those changes. Once the pull request is ready, I'll request review from you.

[Copilot]

@redpanda-f I've opened a new pull request, #54, to work on those changes. Once the pull request is ready, I'll request review from you.

[redpanda-f]

@rvagg request re-review, added testing surrounding ENV_VAR