shell.Add always wraps a folder even only one file is added

[CsterKuroi]

This is a big overhead for systems that often add a single file when use go-ipfs-api.

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[CsterKuroi]

https://github.com/ipfs/go-ipfs-api/blob/42a3388734299b72d7719a4f1b728d78e0a2e164/add.go#L65

[guseggert]

This should be addressed as part of https://github.com/ipfs/kubo/issues/9124

[lidel]

We will not spend time on improving this library, let's continue in https://github.com/ipfs/kubo/issues/9124