The original implementation unpacked the downloaded provider .zip files directly in the Terraform plugin cache directory. This made the `terraform init` command prone to race conditions when multiple Terraform modules using the same cache were downloading, checksumming, and validating the provider files at the same time.
This is a serious problem in CI workflows, as it forces developers to choose between initializing modules serially and using the cache, or initializing modules in parallel, but download the same modules every time, increasing the consumed bandwidth.

This change unpacks the .zip files in a temporary directory with a unique name inside the plugin cache directory, and only then moves the files to the expected location.

This change is inspired by this PR: hashicorp#33479