Fix/command duration precision

[BarbUk]

Description

Change back the precision of command duration to deciseconds instead of nanoseconds

Motivation and Context

The precision of command duration is not accurate with nanoseconds or microseconds.
Using deciseconds gave the best result when I initially developed this functionality.

Moreover, the current calculations are not valid:

deciseconds="$((10 - (command_start_deciseconds - current_time_deciseconds)))"

This can only be used accurately with deciseconds.

If anyone is interested, I can modify this PR to introduce a configuration giving user the choice of precision to use:

• seconds only
• deciseconds
• microseconds
• etc.

How Has This Been Tested?

Calculation have been verified and display has been tested with barbuk theme (cf screenshot).

Screenshots (if appropriate):

Before:

After:

Types of changes

• 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 change)

Checklist:

• My code follows the code style of this project.
• If my change requires a change to the documentation, I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• If I have added a new file, I also added it to clean_files.txt and formatted it using lint_clean_files.sh.
• I have added tests to cover my changes, and all the new and existing tests pass.

[NoahGorny]

LGTM, thanks @BarbUk !

[gaelicWizard]

Thanks @BarbUk!