Improve repr of pygit2.hash

At present hash and pygit2.hash have the same repr. We can tell them apart by looking at the __module__ attribute. But not their type.

Python 3.10.6 (main, Nov 14 2022, 16:10:14) [GCC 11.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pygit2
>>> hash, pygit2.hash
(<built-in function hash>, <built-in function hash>)
>>> id(hash) - id(pygit2.hash)
2918112
>>> pygit2.hash.__module__
'pygit2._pygit2'
>>> hash.__module__
'builtins'
>>> type(hash), type(pygit2.hash)
(<class 'builtin_function_or_method'>, <class 'builtin_function_or_method'>)
>>> 

This will confuse anyone who relies on repr to check that they are using the correct hash function.

首先重现 issue 中的 Python REPL 示例，并检查 pygit2.hash 背后的实现。确定其 repr 当前如何与 built-in hash 相匹配，然后修改该表示形式以区分这两个函数，并在 Python 中验证修改后的输出。