Remove anyhow dependency

[piegamesde]

Anyhow is a great error handling crate for applications, but libraries should prefer brining their own error types instead. For example, I switched from anyhow to eyre, and adding the cli-clipboard dependency would reintroduce anyhow which I don't necessarily want/need.

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I'm just noticing wl-clipboard-rs also depends on failure, which means I now depend on three(!) similar error handling crates. I'll open an upstream issue there too.