Fix business days counting in before/after methods

[guillaumebihet]

Reference

Issue 196

Description

Problem:

The counting of business days is inconsistent in before and after methods depending on whether the start date is a workday or not.

When starting on a workday:

> 5.business_days.before(Date.new(2025, 1, 15))
=> Wed, 08 Jan 2025

This only counts 4 workdays (Tue 14, Mon 13, Fri 10, Thu 9), instead of 5.

But when starting on a non-workday:

> 5.business_days.before(Date.new(2025,02,15))
=> Fri, 07 Feb 2025

This correctly counts 5 workdays (Fri 14, Thu 13, Wed 12, Tue 11, Mon 10).

See also #196 (comment) for a more detailed explanation.

Solution:

Move one day first before starting the count:

time -= 1.day  # For before()
# or
time += 1.day  # For after()

This ensures we never count the start date itself, making the behavior consistent in all cases.