Convert `IGDBBaseHandler` methods to be asynchronous, and use an `httpx`
async client, instead of `requests` sync client.
This change also removes the direct dependency with `requests`, as the
project no longer uses it, preferring `httpx` instead.
For filesystem resource handler, `requests` calls have been replaced
with `httpx`, and file I/O has been replaced with `anyio` utils.
The existing approach to save covers and screenshots, by calling
`shutil.copyfileobj` with the raw response is no longer needed. `httpx`
does not provide a file-like object when streaming [1], so there's no
easy drop-in replacement.
However, the applied solution correctly builds the file iteratively, by
consuming the response in chunks.
[1] https://github.com/encode/httpx/discussions/2296
`os.walk` is a generator that can iteratively navigate from the
specified path, top-bottom. However, most of the calls to `os.walk` in
the project cast the call to `list()`, which makes it traverse the path
and recursively find all nested directories.
This is commonly not needed, as we end up just using a `[0]` index to
only access the root path.
This change adds a few utils that simplifies listing files/directories,
and by default does it non-recursively. Performance gains shouldn't be
noticeable in systems with high-speed storage, but we can avoid the edge
cases of users having too many nested directories, by avoiding unneeded
I/O.
