This change installs and configures the `mod_zip` nginx module [1],
which allows nginx to stream ZIP files directly.
It includes a workaround needed to correctly calculate CRC-32 values for
included files, by including a new `server` section listening at port
8081, only used for the file requests to be upstream subrequests that
correctly trigger the CRC-32 calculation logic.
Also, to be able to provide a `m3u` file generated on the fly, we add a
`/decode` endpoint fully implemented in nginx using NJS, which receives
a `value` URL param, and decodes it using base64. The decoded value is
returned as the response.
That way, the contents of the `m3u` file is base64-encoded, and set as
part of the response, for `mod_zip` to include it in the ZIP file.
[1] https://github.com/evanmiller/mod_zip
`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.
