Fix max number of tokens for synthetic data generator

[jackcook]

When using prompt_tokens_max (and not using prompt_tokens_stdev), there will occasionally be one token more than the maximum number specified. This can be tested as follows:

from guidellm.utils import IntegerRangeSampler

MIN_VALUE = 5
MAX_VALUE = 15

irs = IntegerRangeSampler(average=(MAX_VALUE - MIN_VALUE) // 2, variance=None, min_value=MIN_VALUE, max_value=MAX_VALUE, random_seed=None)
it = iter(irs)

for _ in range(10000):
    assert next(it) != 16

The assertion will fire, despite the max being set to 15. This happens because random.randint, which is used by IntegerRangeSampler, generates numbers up to and including the max value it is given. This PR fixes that.

[markurtz]

Looks great, thanks @jackcook!