Remove public 'fname' learner attribute about adaptive HOT 3 CLOSED

def combo_fname(val):
    return '__'.join([f'{k}_{v}' for k, v in val.items()])

combos = adaptive.utils.named_product(a=[1, 2], b=[1])
learners = []
for combo in combos:
    l = Learner(partial(f, combo=combo))
    l.fname = combo_fname(combo)
    learners.append(l)
learner = BalancingLearner(learners)
learner.load(folder='data_folder')

combos = adaptive.utils.named_product(a=[1, 2], b=[1])
learners = {Learner(partial(f, combo=combo)): combo for combo in combos}

def combo_fname(learner):
    val = learners[learner]
    return 'data_folder/' + '__'.join([f'{k}_{v}' for k, v in val.items()])

learner = BalancingLearner(list(learners.keys()))
learner.load(fname=combo_fname)

def combo_fname(learner):  # this function is pure
    val = learner.function.keywords  # from functools.partial
    return 'data_folder/' + '__'.join([f'{k}_{v}' for k, v in val.items()])

combos = dict(a=[1, 2], b=[1])
learner = BalancingLearner.from_product(f, Learner1D, dict(bounds=(-1, 1)), combos)
learner.load(fname=combo_fname)