Truncate Right (#841)

* feat(tokenizers): add truncate test case

* !feat(tokenizer): truncate right

* refacto(tokenizers): clippy

* feat(bindings): update bindings for truncate()

* fix(tokenizers): remove unsafe code

* refacto(tokenizers): truncate direction

* truncate direction enum
* compute parts ranges beforehand
* 2n space because encoding is dropped at the end of procedure
* update bindings
* add pip install in python bindings' make test

* fix(node): clippy asks to use unwrap_or_else

* fix(node): lint

* refacto(tokenizers): replace Vec<Range<usize>> by Vec<(usize, usize)>

* refacto(bindings): add match syntax

* refacto(tokenizers): use mem::replace instead of mem::swap

* refacto(tokenizers): assign value the normal way

bindings/python/py_src/tokenizers/__init__.pyi

@@ -286,7 +286,7 @@ class Encoding:
             :obj:`List[str]`: The list of tokens
         """
         pass
-    def truncate(self, max_length, stride=0):
+    def truncate(self, max_length, stride=0, direction="right"):
         """
         Truncate the :class:`~tokenizers.Encoding` at the given length
 
@@ -299,6 +299,9 @@ class Encoding:
 
             stride (:obj:`int`, defaults to :obj:`0`):
                 The length of previous content to be included in each overflowing piece
+
+            direction (:obj:`str`, defaults to :obj:`right`)
+                Truncate direction
         """
         pass
     @property