Add Cohere embeddings integration

[morganmcg1]

This PR adds support for Cohere embeddings integration to Weave.

Changes:

• Added embeddings wrapper functions for both sync and async clients
• Added tests for embeddings functionality
• Generated test cassettes
• Added proper handling of usage data in meta field

The implementation follows the same pattern as the OpenAI embeddings integration.

Example trace: https://wandb.ai/morgan/cohere-embeddings-example/r/call/01949331-83e2-7e82-b33a-ddd221da25b6

Example usage:

import weave
import cohere

# Initialize weave with a project name
client = weave.init("cohere-embeddings-example")

# Initialize Cohere client
co = cohere.Client("your-api-key")

# Create some example texts
texts = [
    "The quick brown fox jumps over the lazy dog",
    "Machine learning is transforming the world",
    "Artificial intelligence and neural networks"
]

# Get embeddings
response = co.embed(
    texts=texts,
    model="embed-english-v3.0",
    input_type="search_document"
)

# Get the traced calls
calls = list(client.get_calls())

# Example traced output:
# Operation name: weave:///morgan/cohere-embeddings-example/op/cohere.Client.embed:EEbjvTp2FQIfCtuX86kEdYio6gsbggWdimA7g2Xj4VE
# Start time: 2025-01-23 12:33:30.444069+00:00
# End time: 2025-01-23 12:33:30.566521+00:00
# Duration: 0.122452 seconds
# Number of embeddings: 3
# Meta information: {
#   "api_version": {"version": "1"},
#   "billed_units": {"input_tokens": 20.0},
#   "warnings": []
# }

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