• pyln-client has a resource leak in UnixSocket.__init__(…) in the fallback path that is executed when the RPC socket path is longer than can fit in a struct sockaddr_un. This was causing file descriptor exhaustion in pytests.
  

  lightning/contrib/pyln-client/pyln/client/lightning.py

  Line 256 in fcd92fe

  dirfd = os.open(dirname, os.O_DIRECTORY | os.O_RDONLY)

• pyln-testing has a resource leak in utils.env(…) when reading config.vars.
  

  lightning/contrib/pyln-testing/pyln/testing/utils.py

  Line 63 in fcd92fe

  lines = open(fname, 'r').readlines()

• pyln-testing has a resource leak in node_factory, as it neglects to call cleanup_files() on the LightningD instances produced by the factory.
• pyln-testing has a resource leak in GossipStore, as it neglects to close the underlying file descriptor when an instance is discarded or when an instance is re-opened.
• Many locations throughout tests/ had file descriptor leaks due to calling open or pathlib.Path.open without using with and without calling close(). These are fixed using with or pathlib.Path.{read,write}_bytes.

Checklist

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• The changelog has been updated in the relevant commit(s) according to the guidelines.
• Tests have been added or modified to reflect the changes.
• Documentation has been reviewed and updated as needed. Not applicable.
• Related issues have been listed and linked, including any that this PR closes. None found.