export symbols using __all__ to avoid typing errors

[Andrej730]

Mentioned in #1322

Explanation on how it works - https://github.com/microsoft/pyright/blob/main/docs/typed-libraries.md#library-interface

Example failing snippet:

import pygit2

# "Repository" is not exported from module "pygit2" PylancereportPrivateImportUsage
def test(repo: pygit2.Repository):
    ...

Wanted to solve that particular error with missing Repository symbol and I'm not very familar with pygit2 repository - so please advice if any symbols should be removed or added.
Currently I've included all symbols that are imported in __init__, except ffi, C (looked like something private), to make it fully compatible with current from pygit2 import * behaviour (definingi __all__ is limiting wild card import).

[jdavid]

import sys
before = set(dir())
from pygit2 import *
after = set(dir())
imported_symbols = after - before
print(len(imported_symbols))

This prints 412, while in this PR __all__ has 127 symbols.
For backwards compatibility you can just put all of them, sorted alphabetically, then I will go through and remove those deemed internal or deprecated.

Also put __all__ at the very end of the file.

[Andrej730]

That's a lot missed symbols! Submitted new commits - first one just added all symbols in A-z order, second one categorized them so it will be easier to discard some specific cateogires and then maintain it.

This is how I was testing it:

Test symbols without __all__ taking effect (__all__ renamed to __all__test):

before = set(dir())
from pygit2 import *

after = set(dir())
imported_symbols = after - before - {"before"}

import pygit2
all_symbols = set(pygit2.__all__test)
print(len(all_symbols)) # 411
print(len(imported_symbols)) # 411
assert len(diff:=(all_symbols - imported_symbols)) == 0, diff
assert len(diff:=(imported_symbols - all_symbols)) == 0, diff

Test with __all__ enabled:

before = set(dir())
from pygit2 import *

after = set(dir())
imported_symbols = after - before - {"before"}

import pygit2
assert len(imported_symbols) == len(set(pygit2.__all__)) == 411
assert set(imported_symbols) == set(pygit2.__all__)