Module metrics 

Monthly shift counts and work/rest tracking.

All functions iterate day-by-day through the target range and call get_shift_type_for_date for each day.

Ported from Flutter shift_metrics.dart and Android shift_metrics.kt.

Functions

consecutive_work_days

Count consecutive work days looking backward from today (inclusive).

count_shift_type_in_month

Count how many days of a given shift type occur in a month.

count_work_days_in_month

Count total working days (Morning + Afternoon + Night) in a month.

days_until_next_rest

Days until the next rest day, starting from tomorrow (excludes today).