Fix: Cache path

[naranjamecanica]

Use pkg-dir to find projects base directory and us path.join to create crossplatform paths.

[vHeemstra]

Thanks for the PR!

Some adjustments:

• Since all paths are normalized using Vite's normalizePath() (so using forward slashes), there's no need for path.join(). Moreover, path.join on Windows would actually insert backward slashes, so I rather not use that to keep consistent (cross-platform) paths.
• Instead of added another package, I would rather add the actual function that gets the package directory. Also, earlier, I tried adding this package, but there was some conflict on the engine/Node versions. pkg-dir only supports Node 18+ (in its package config only).
• Also, I would like to add the option to choose the cacheDir:
  • (default) <packageRoot>/node_modules/.cache/vite-plugin-imagemin/
  • relative path string, like some-dir, would become <root>/some-dir/
  • absolute path string
• Maybe add the option clearCache, so users can make their own logic in their config for clearing the cache.

I will create a new branch with these functionalities. Any additional suggestions can be PR'd there.

https://github.com/vHeemstra/vite-plugin-imagemin/tree/improve-cache-handling

[vHeemstra]

I made a new branch with all the changes mentioned above and created a new PR: #10

Can you have a look? If you have any suggestions/changes/etc, please feel free to comment there. (Or create a PR to that branch.)

Otherwise, I will merge the branch somewhere this week.