Get cursor position support

[ds-hystax]

Hi! I'm currently using json-stream to parse a funky file that has a JSON header with binary data afterwards. The library handles such files without issues, but I would like to know the position where JSON ends and data starts.

I've managed to do it using the following code, but it's kinda hacky:

import json_stream
from json_stream.select_tokenizer import rust_tokenizer_or_raise

with open('test.bin', 'rb') as test_file:
    tokenizer = rust_tokenizer_or_raise()(test_file, correct_cursor=True)
    header = json_stream.load(self._file, tokenizer=lambda _: tokenizer)
    # parse header here...
    tokenizer.park_cursor()
    binary_start = test_file.tell() + 1
    print(binary_start)

Having a cleaner and documented way to do it in json-stream would be very nice.