fix!: Smart remove rule ""Keep one snapshots per week or the last week"

[buhtz]

The smart remove rule "Keep one snapshots per week or the last week" now use full calendar weeks without losing snapshots in between.

The previous behavior was confuse and not clear.

Replace PR

• fix: Smart Remove behavior to really "keep one snapshot per week for n weeks" #1819

That PR is in preparation for meta issue

• Revise Auto- and Smart-Remove feature #1945

Will merge it soon to go further with

• fix: Improve "Auto-remove" ("Remove & Retention") GUI and its documentation #2000

Might fix

• Weekly snapshots not being retained #1094