Make input/output structs implement closeable when these have streaming members

[sugmanue]

…

Issue #, if available:

Description of changes:

Make input/output structs implement Closeable when these have streaming members. E.g.,

    /**
     * Closes the underlying event stream.
     */
    @Override
    public void close() {
        if (stream != null) {
            stream.close();
        }
    }

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