Include all LoadLibrary() failures in exception chain

[bgilbert]

If libopenslide.so.1 fails to load, we want to report that exception too, not just the fact that libopenslide.so.0 doesn't exist. Make try_load() recursive rather than iterative, allowing Python's exception chaining to handle this automatically. Reported by @govinda-kamath; thanks!

Also use explicit exception chaining during any conversion of exception types. This changes Python's exception chain reporting to make it clear that the new exception was not an unrelated failure while handling the original one, but rather the direct cause of it.

[openslide-bot]

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[bgilbert]

This now produces exception chains like this:

Traceback (most recent call last):
  File "/home/bgilbert/.local/lib/python3.12/site-packages/openslide/lowlevel.py", line 76, in try_load
    return cdll.LoadLibrary(names[0])
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.12/ctypes/__init__.py", line 460, in LoadLibrary
    return self._dlltype(name)
           ^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.12/ctypes/__init__.py", line 379, in __init__
    self._handle = _dlopen(self._name, mode)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^
OSError: libopenslide.so.1: cannot open shared object file: No such file or directory

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/bgilbert/.local/lib/python3.12/site-packages/openslide/lowlevel.py", line 116, in _load_library
    return try_load(['libopenslide.so.1', 'libopenslide.so.0'])
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/bgilbert/.local/lib/python3.12/site-packages/openslide/lowlevel.py", line 82, in try_load
    return try_load(remaining)
           ^^^^^^^^^^^^^^^^^^^
  File "/home/bgilbert/.local/lib/python3.12/site-packages/openslide/lowlevel.py", line 76, in try_load
    return cdll.LoadLibrary(names[0])
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.12/ctypes/__init__.py", line 460, in LoadLibrary
    return self._dlltype(name)
           ^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.12/ctypes/__init__.py", line 379, in __init__
    self._handle = _dlopen(self._name, mode)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^
OSError: libopenslide.so.0: cannot open shared object file: No such file or directory

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/bgilbert/.local/lib/python3.12/site-packages/openslide/__init__.py", line 35, in <module>
    from openslide import lowlevel
  File "/home/bgilbert/.local/lib/python3.12/site-packages/openslide/lowlevel.py", line 125, in <module>
    _lib = _load_library()
           ^^^^^^^^^^^^^^^
  File "/home/bgilbert/.local/lib/python3.12/site-packages/openslide/lowlevel.py", line 118, in _load_library
    raise ModuleNotFoundError(
ModuleNotFoundError: Couldn't locate OpenSlide shared library. Try `pip install openslide-bin`. https://openslide.org/api/python/#installing