Refactor stimulus protocol retrieval in MakieRecipes.jl for improved clarity

- Replaced direct access to the stimulus protocol with a dedicated function, enhancing code readability and maintainability.
- This change supports better integration with the existing plotting functions and ensures consistent handling of stimulus data.

Author: mattar13

src/PhysMakie/MakieRecipes.jl

@@ -250,7 +250,7 @@ function Makie.plot!(st::StimulusTiming)
         return st # Return the plot object early
     end
 
-    stim_protocol = exp.HeaderDict["StimulusProtocol"]
+    stim_protocol = getStimulusProtocol(exp)
 
     # Get stimulus start and end times
     # Ensure these functions are available and work with stim_protocol object