Use a more generic FS interface

[jsvk]

fs.FS is an interface *embed.FS implements, so switching to this should offer more flexibility because you can still use *embed.FS, but you can now also use your own instances of fs.FS implementations.

This is extra useful if you're creating your fs.FS at runtime, as it's not easy to create an *embed.FS at runtime.

[rookie-luochao]

good job, thanks for your advice