The BaseRepository.diff signature takes 'flags: DiffOption = ...', not
'flag', but the docstring's Keyword arguments block listed 'flag'.

Closes #1138

Since its introduction in commit 81520c9 (Update to libgit2 v0.23),
the reflog identity getter (Repository.ident) has been
passing the (char **) variables directly to ffi.string()
as C-strings, when they really are pointers to C-strings.
Fix by dereferencing the pointer to a C-string first.

Furthermore, Repository.ident assumes that said variables
hold valid C-strings, when the reflog identity is initialized
to NULL, and can be explicitly set to such with `set_ident
(None, None)`.  So map None to ffi.NULL (which maybe_string()
happens to already do, so I simply delegated to that...).

I also added a few regression tests to ensure neither issue
shows up again.

Signed-off-by: Ethan Meng <[email protected]>

Since set_ident() already has type annotations, it
seems fitting that we adorn ident() with those too. :)

Also, to_bytes() is perfectly capable of mapping None
to ffi.NULL, so the parameters on set_ident() should be
`str | None` (aka Optional[str]).

Signed-off-by: Ethan Meng <[email protected]>

Repository.default_signature is a read-only descriptor,
not a getter method.

Signed-off-by: Ethan Meng <[email protected]>

Fixes #1458

Fixes #1454

Assisted-by: Kimi-k2.6

Assisted-by: Kimi-k2.6

Assisted-by: Kimi-k2.6