When connected to file, close the file if done reading it

[stasostyk]

When using a file as a mavlink connection (DFReader_binary), the file is never closed and there is no close method provided. As a result, the file is constantly kept open until the python process entirely ends, which could lead to resource leaks, data corruption, and does not allow for doing other operations on the file.

A close method should be added, and when parsing through all log messages and reaching the end, the file should be closed.

Additionally, the close method should be available to be called at any point.