Remove EOL in command channel message logs

Description

FTP commands and responses end with CRLF, which is logged, resulting in a double line return.

This removes the EOL from message to fix it.

FTP specifies CRLF as the only valid EOL marker. We know we use it, so I trimmed the end CRLF in sent commands. For response, I went for a safer approach in case some server don't use proper CRLF.

Let me know if you have a better idea than "CC OUT" / "CC IN" for control channel in/out ! ("CMD"/"RESP", "CC ->"/"CC <-" ...)

Type of change

Please select relevant options.

[x] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
[ ] This change requires a documentation update

Checklist

[x] My code follows the contribution guidelines of this project
[x] I have performed a self-review of my own code
[x] I have commented my code, particularly in hard-to-understand areas
[x] My changes generate no new warnings
[x] I formatted the code with cargo fmt
[x] I linted my code using cargo clippy and reports no warnings
[x] I have added tests that prove my fix is effective or that my feature works
[x] I have introduced no C-bindings
[x] I increased or maintained the code coverage for the project, compared to the previous commit

Acceptance tests

wait for a project maintainer to fulfill this section...

[x] regression test: log lines are displayed correctly

veeso / suppaftp