Development: Make iter_backwards work on file-like objects

[priitlatt]

In utilities package codemagic.utilities.backwards_file_reader there is a function iter_backwards that can be used to iterate over lines in file from bottom to top.
Currently it only works with files that are saved to disk and the function takes file path (as a string or pathlib.Path object) as an argument.

But in reality the files are not always saved to the disk, and can be stored in-memory. In such cases the path is not available and as a result iter_backwards function cannot be used.

Changes in this PR add support to iterate lines on file-like objects too.

Examples of updated usage:

• Iterate backwards over a file that is saved to disk

import tempfile

from codemagic.utilities.backwards_file_reader import iter_backwards

with tempfile.NamedTemporaryFile('w') as tf:
    tf.write('one\ntwo\nthree')
    tf.flush()
    print(list(iter_backwards(tf.name)))  # prints ['three', 'two', 'one']

• Iterate backwards over an in-memory file

import io
import tempfile

from codemagic.utilities.backwards_file_reader import iter_backwards

sio = StringIO('one\ntwo\nthree')
print(list(iter_backwards(sio)))  # prints ['three', 'two', 'one']

with tempfile.TemporaryFile('r+') as tf:
    tf.write('one\ntwo\nthree')
    tf.flush()
    print(list(iter_backwards(tf)))  # prints ['three', 'two', 'one']