fix: Combine contiguous active periods

[joshlarson]

Changes

Before is on the left, After is on the right. Note that:

• The OL disruptions have narrower date ranges now, based on not combining the whole active period range anymore. (For instance, the "This week" OL disruption only goes until Feb 28)
• The BL disruptions got split up into each weekend, instead of spanning the whole week.
• Disruptions are still not sorted correctly within their buckets - that's out of scope for this PR.

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Asana Ticket: [PW] Fix contiguous active period logic

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TODO

• Tests are a bit flaky - I goofed something in my Faker setup
• Docs have some sentence fragments
• Doctest or regular test for DateTime.shift/2

[thecristen]

Thanks!!

[anthonyshull]

Should be alphabetical with the ones below.

[joshlarson]

Woops - good catch thanks!