Name of FitParameter should not be mutable

[redeboer]

Bug description

The FitParameters class uses the names of all FitParameter instances it contains as keys. However, it's still possible to change the FitParameter.name after it has been added.

How to reproduce?

import expertsystem as es

result = es.generate_transitions(
    initial_state=[("J/psi(1S)", [-1, 1])],
    final_state=["gamma", "pi0", "pi0"],
    allowed_intermediate_particles=["f(0)(980)", "f(0)(1500)"],
    allowed_interaction_types=["strong", "em"],
)
model = es.generate_amplitudes(result)
for particle in result.get_intermediate_particles():
    model.dynamics.set_breit_wigner(particle.name)

model.parameters["Width_f(0)(980)"].name = "trolling you"
assert "trolling you" in model.parameters  # <-- fails

Expected behavior

It should not be possible to change the name of a FitParameter.

[redeboer]

Irrelevant since #454, even though it should be noted that sympy.Symbol shows the same behaviour.