bernoulli_rng - add signature `ints bernoulli_rng(real theta)`

Description

Add implementation of bernoulli_rng which generates an array of bernoulli outcomes for a single value of theta.

Example

Currently, it is necessary to use a loop, e.g.

  real theta = beta_rng(1, 1);
  array[N] int y; 
  for (n in 1:N) {
    y[n] = bernoulli_rng(theta);
  }

The vectorized alternative is:

  real theta = beta_rng(1, 1);
  array[N] int y; 
   y = bernoulli_rng(rep_array(theta, N_obs));

This is problematic for 2 reasons:

• requires extra memory allocation for the array of thetas
• not as easy to grok

Expected Output

It would be nice to be able to do the following:

  real theta = beta_rng(1, 1);
  array[N] int y; 
   y = bernoulli_rng(rtheta);

Current Version:

v4.8.1

Start by locating the existing bernoulli_rng implementation and its vectorized RNG tests. Add coverage for a scalar theta producing an array of outcomes, then run the relevant bernoulli_rng tests; done means the new signature works without constructing an array of repeated theta values.