Transfer - Improve time estimation algorithm

[yahavi]

• All tests passed. If this feature is not already covered by the tests, I added new tests.
• All static analysis checks passed.
• This pull request is on the dev branch.
• I used gofmt for formatting the code before submitting the pull request.

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Introduce a new time estimation algorithm for the jf rt transfer-files command:
Divide the transferred bytes in the ongoing process by the remaining size.

The time estimation will only show up if these conditions are fulfilled:

1. Five minutes have elapsed since the transfer started.
2. A minimum of one file has been successfully transferred.
3. The calculated speed is at least one byte per second.