* Fixing a bug where long tokenizer files would be incorrectly
deserialized
- Add a bunch of tests to check deserialization behaviour
- One tests also confirms current Single deserialization of Sequence.
* Better test locations for Windows + no file dependency in Python binding
Rust side.
* Adressing @n1t0 comments.
- Leaving the one that checks that sampling follows the expected
distribution.
- Marking the python Unigram.train(..) test as slow
- The python Unigram.train(..) test now uses `big.txt` file.