RV: Samples do not know of RV name

[nabriis]

Description

The samples object does not include (or at least the histogram plot does not) the variable name of the random variable

Example to reproduce

Provide a code example to reproduce the bug

from cuqi.distribution import Beta, Gamma

# Define the shape parameters of the Beta distribution
a1, a2 = 3, 2

# Step 1: Directly define a Beta distribution
z_ref = RandomVariable(Beta(a1, a2))

# Step 2: Construct the Beta distribution using Gamma random variables
x = RandomVariable(Gamma(a1, 1))  # X ~ Gamma(a1, 1)
y = RandomVariable(Gamma(a2, 1))  # Y ~ Gamma(a2, 1)
z = x / (x + y)                   # Z ~ Beta(a1, a2)

# Step 3: Sample from both distributions
z_samples = z.sample(10000)       # Samples from constructed Beta distribution
z_ref_samples = z_ref.sample(10000)  # Samples from direct Beta distribution

# Step 4: Plot histograms of the samples for comparison
z_samples.hist_chain([0], bins=100)
z_ref_samples.hist_chain([0], bins=100)