CLIP tweaks

[brimoor]

Small editing pass over @Rusteam's amazing work from #1691.

Example usage below. Zero shot prediction is so cool 🔥 🤗

import fiftyone as fo
import fiftyone.zoo as foz

dataset = foz.load_zoo_dataset(
    "coco-2017",
    split="validation",
    max_samples=51,
    shuffle=True,
    seed=51,
)

# Make zero-shot predictions with custom classes!
model = foz.load_zoo_model(
    "clip-vit-base32-torch",
    text_prompt="A photo of a",
    classes=["person", "dog", "cat", "bird", "car", "tree", "chair"],
)

dataset.apply_model(model, label_field="predictions")

session = fo.launch_app(dataset)

[ehofesmann]

LGTM! Very excited to have CLIP in the zoo!