Support Tensor Parallel in Python API

[rasbt]

Adds tensor parallel support for the Python API:

from litgpt.api import LLM

llm = LLM.load(
    model="microsoft/phi-2",
    distribute=None
)

llm.distribute(generate_strategy="tensor_parallel", devices=2)

llm.generate(prompt="What do llamas eat?", top_k=1)