Updating a Dist with a function fails silently

[cliffckerr]

import starsim as ss

p = 0.123

def prob_func(module=None, sim=None, size=None):
    return p

d1 = ss.HIV(init_prev=p) # fine
d2 = ss.HIV(init_prev=ss.bernoulli(p)) # fine
d3 = ss.HIV(init_prev=prob_func) # NOT FINE
d4 = ss.HIV(init_prev=ss.bernoulli(prob_func)) # fine
di = [d1, d2, d3, d4]

sims = [ss.Sim(diseases=d) for d in di]
sims = ss.parallel(sims).sims
for s in sims:
    print(s.diseases.hiv.pars.init_prev)

gives

ss.bernoulli(pars_hiv_init_prev, pars={'p': 0.123}) # fine
ss.bernoulli(pars_hiv_init_prev, pars={'p': 0.123}) # fine
ss.bernoulli(pars_hiv_init_prev, pars={'p': 0.05}) # WRONG, no error
ss.bernoulli(pars_hiv_init_prev, pars={'p': <function prob_func at 0x72d70041afc0>}) # fine

Should either just work, or raise an exception

[cliffckerr]

Now raises an exception, but should work

[cliffckerr]

Closed by #778