add initial attempt for fixing parameters and broadcasting

[Transurgeon]

This PR adds minimal changes to support broadcast(parameter).
More generally, I think this will also allow constant parameters to appear as the param_source for the three bivariate atoms we have.

To clarify the language, by constant parameters I mean any arbitrary expression involving cp.parameters (or cp.constants)
which also satisfies the .is_constant() attribute in Python.

This means that we will form an matmul/multiply node where the param_source is a tree rather than a single node.
The fix is to simply call forward on the param_source expression and then use it's values for the bivariate atom.

[Transurgeon]

@dance858 is this similar to what you had in mind for this issue?
also the CI only runs valgrind for some reason.. should we change it so that everything runs on every PR?
we have something like this in the CI:

  on:                                                                                      
    push:                                                                                  
      branches: [main, development]                                                        
    pull_request:                                                                        
      branches: [main, development]     

but I wonder if we could make it more general to any branch or something.