…the correct BPE model

The _decode_native_and_split function decodes encoded BPE tokens into their corresponding byte arrays and returns a vector of vectors of bytes. The split_by_token_with_special_tokens function takes in a string, encodes it using the BPE model, and then decodes the encoded tokens into a vector of strings. This allows for tokenizing a string and returning the decoded tokens using the correct BPE model. Added a corresponding test (cl100k_split_test) to tests/tiktoken.rs.

Add the "Eq" trait to the "ChatCompletionRequestMessage" struct to allow for easy comparison with other structs.

Add a new method to CoreBPE, split_by_token_with_special_tokens(), which takes a string slice containing the text to be tokenized, encodes it using the BPE model, and decodes the encoded tokens into a vector of strings. The resulting iterator yields each token as a Result<String> to handle decoding errors. The method includes a test to ensure its correctness.