fix(plan): show each item of a changed list property

[GClunies]

What

snowcap plan now shows a changed list property one item per row, with the before and after values side by side. A dict item shows as key: value pairs. A non-list value renders as before.

Why

The plan rendered a changed list as one table cell. Past 60 characters, the cell collapsed to <1 line, N chars>. The reviewer could see that something changed but not what changed. A one-word change to a resource monitor trigger (#86) looked like this:

│ triggers │ <1 line, 157 chars> │ <1 line, 158 chars> │

With this change:

│ triggers │ threshold: 50, action: NOTIFY  │ threshold: 50, action: NOTIFY   │
│          │ threshold: 75, action: NOTIFY  │ threshold: 75, action: NOTIFY   │
│          │ threshold: 90, action: NOTIFY  │ threshold: 90, action: NOTIFY   │
│          │ threshold: 100, action: NOTIFY │ threshold: 100, action: SUSPEND │

This applies to every list property, for example allowed_ip_list on network policies and indexes on hybrid tables. Each item shows in full. Only a multiline item still collapses, because the table cannot show a newline.

Items pair by position. If an item is inserted mid-list, the rows after it differ too. This keeps the change small. Lists that Snowcap already sorts (for example resource monitor triggers in #86) line up item by item.

Tested

Check	Result
tests/test_blueprint.py::test_plan_text_shows_each_item_of_a_changed_list (network policy IPs; hybrid table indexes with an item longer than 60 chars)	fails before, passes after
Unit suite pytest tests --ignore=tests/integration	2229 passed
make lint	clean
snowcap plan against a live account with one changed ACCOUNT_RM trigger (on top of #86)	output shown above