Refactor README and Vicinity class to support any serializable item type

[davidberenstein1957]

I was playing around and realised the items don't necessarily need to be strings.

Update

• Updated README.md to clarify that items can be strings or other serialisable objects.
• Modified the Vicinity class to accept a broader range of item types by changing type hints from str to Any in several methods.
• Enhanced the insert and delete methods to handle non-string tokens appropriately, ensuring that items can be checked and managed regardless of their type.

Question
Also, why do we use tokens as argument names for items in the insert and delete methods?

Example
Something like the following works now. Slower during insert and deletion but I would say the flexibility is worth it.

import numpy as np

from vicinity import Backend, Metric, Vicinity

# Create some dummy data
items = [
    {"name": "triforce", "id": 0},
    {"name": "master sword", "id": 1},
    {"name": "hylian shield", "id": 2},
    {"name": "boomerang", "id": 3},
    {"name": "hookshot", "id": 4},
]


vectors = np.random.rand(len(items), 128)

# Initialize the Vicinity instance (using the basic backend and cosine metric)
vicinity = Vicinity.from_vectors_and_items(
    vectors=vectors, items=items, backend_type=Backend.BASIC, metric=Metric.COSINE
)

# Create a query vector
query_vector = np.random.rand(128)

# Query for nearest neighbors with a top-k search
results = vicinity.query(query_vector, k=3)

# Query for nearest neighbors with a threshold search
results = vicinity.query_threshold(query_vector, threshold=0.9)

vicinity.delete([items[0], items[1], items[2], items[3], items[4]])
vicinity.insert(items, vectors)
# Query with a list of query vectors
query_vectors = np.random.rand(5, 128)
results = vicinity.query(query_vectors, k=3)
print(results)

vicinity.save("my_vector_store", overwrite=True)
vicinity = Vicinity.load("my_vector_store")

results = vicinity.query(query_vectors, k=3)
print(results)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files with missing lines	Coverage Δ
tests/conftest.py	100.00% <100.00%> (ø)
tests/test_vicinity.py	100.00% <100.00%> (ø)
vicinity/vicinity.py	98.62% <100.00%> (+0.94%)	⬆️

[stephantul]

This looks good, thanks! One improvement I see is that we can explicitly throw a ValueError on trying to save if the items are not JSON serializable. e.g., by catching a JsonEncodeError and giving a more informative warning.

Another improvement is the typing, but I'll do that in a follow-up because I actually don't know what the best way is 💀