Monitor: show timestamp when receiving messages

[alessio-perugini]

Describe the request

When opening the serial monitor with arduino-cli monitor -p /dev/ttyACM0 would be cool to prefix the timestamp of a message received from the serial.
We can add a new flag like --show-timestamp that enables such a feature.

Expected output:

[2023-09-13 16:55:22] Message from serial
[2023-09-13 16:55:25] another message
[2023-09-13 16:55:30] a
[2023-09-13 16:55:35] bcd

Describe the current behavior

When we receive a message from the serial monitor we just show them without prefixing the timestamp.

Arduino CLI version

Operating system

Linux

Operating system version

Ubuntu 23.04

Additional context

No response

Issue checklist

• I searched for previous requests in the issue tracker
• I verified the feature was still missing when using the nightly build
• My request contains all necessary details

[zvonler]

Just opened a PR that I believe resolves this issue. This is my first time writing any Go code (except for the sample program I used to work this out), so please check it carefully and let me know what can be better.

The intent is to print a timestamp before the first character of each line. Any characters received without an included newline are still echoed to the output immediately, and only the first character received after each newline will cause the timestamp output.

#2336