refactor(commands): trim end of `pipe`-like output

[RoloEdits]

Current pipe-like commands, pipe, insert-output, and append-output, return directly what stdout had, which usually includes a newline. This can limit its efficiency in the editor as when someone would want to run the same command on many selections, the additional whitespace can become cumbersome to manually trim.

This PR trims all whitespace from the end of the output. This was mainly chosen do to the simplicity of the change, but even when testing an iteration where only a single newline was removed, it felt more inline with expectations and so was chosen for the final change.

pipe:exa

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xtask
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Closes: https://github.com/helix-editor/helix/issues/10912

[RoloEdits]

I'm unsure if I implemented the change in full completeness, as the exiting logic is kind of hard to understand. When trying the commands in the editor, this worked fine:

        let output = if let Some(output) = shell_output.as_ref() {
            output.clone()
        } else {
            let fragment = range.slice(text);
            match shell_impl(shell, cmd, pipe.then(|| fragment.into())) {
                Ok(result) => {
                    if !pipe {
                        shell_output = Some(result.clone());
                    }
-                    result
+                    Tendril::from(result.trim_end())
                }
                Err(err) => {
                    cx.editor.set_error(err.to_string());
                    return;
                }
            }
        };

But the test failed.

When adding this, the test passed:

        let output = if let Some(output) = shell_output.as_ref() {
-           output.clone()
+           Tendril::from(output.trim_end())
        } else {
            let fragment = range.slice(text);
            match shell_impl(shell, cmd, pipe.then(|| fragment.into())) {
                Ok(result) => {
                    if !pipe {
                        shell_output = Some(result.clone());
                    }
                    result
                    Tendril::from(result.trim_end())
                }
                Err(err) => {
                    cx.editor.set_error(err.to_string());
                    return;
                }
            }
        };

But still not sure if shell_output = Some(result.clone()); needs to be done as well?

edit:

Changed to this and it worked with tests passing:

        let output = if let Some(output) = shell_output.as_ref() {
            output.clone()
        } else {
            let fragment = range.slice(text);
            match shell_impl(shell, cmd, pipe.then(|| fragment.into())) {
                Ok(result) => {
+                    let result = Tendril::from(result.trim_end());
                    if !pipe {
                        shell_output = Some(result.clone());
                    }
                    result
                }
                Err(err) => {
                    cx.editor.set_error(err.to_string());
                    return;
                }
            }
        };