How can I get a Rich Text formula field to display without wrapping?

Use an HTML table, and specify the "nowrap" attribute for the cell. 

See example here:https://www.w3schools.com/tags/tryit.asp?filename=tryhtml_td_nowrap

Code from URL above is pasted below, modified for a single cell. 

<table>    <tr>
      <td nowrap>
         Never increase, beyond what is necessary, the number of entities required to explain anything
      </td>
   </tr>
</table>

Note that the nowrap attribute is not supported in HTML5, and CSS is advised instead.  I'll leave it up to you to apply that how you need it.