weather/envcan: Fix handling of non-continuous hourly folder list

Reason for the change

The previous code assumed the provider would always have a continuous list of hourly folders that contain the forecast files. This is the case most of the times, but I found an instance where this list had an odd '23' folder leftover from the day before.

This was probably a small bug on the provider's side, but it would make the forecast fail for users in that region the whole day.

Let's handle this in a more robust way, by storing the whole sorted list of folders and following it along.

Test plan

It depends on a specific "bug" on the provider's site, that only happens some days on some regions (but it has already happened twice in the last 4 days), when the page at https://dd.weather.gc.ca/today/citypage_weather/ON/ includes a folder for 23 hours

1. In the Weather Widget set the location to "Toronto, ON (Evironment Canada)"

BEFORE

There is no data in the 23 folder, so we naïvely try with 22 which doesn't exists, failing to fetch the correct file

kde.dataengine.ion.envcan: Fetching weather URL: "https://dd.weather.gc.ca/today/citypage_weather/ON/"
kde.dataengine.ion.envcan: Fetching weather URL: "https://dd.weather.gc.ca/today/citypage_weather/ON/23/"
kde.dataengine.ion.envcan: Fetching weather URL: "https://dd.weather.gc.ca/today/citypage_weather/ON/22/"

AFTER

We have stored the list of available folders, so after 23 we correctly try on 12

kde.dataengine.ion.envcan: Fetching weather URL: "https://dd.weather.gc.ca/today/citypage_weather/ON/"
kde.dataengine.ion.envcan: Fetching weather URL: "https://dd.weather.gc.ca/today/citypage_weather/ON/23/"
kde.dataengine.ion.envcan: Fetching weather URL: "https://dd.weather.gc.ca/today/citypage_weather/ON/12/"
kde.dataengine.ion.envcan: Fetching weather URL: "https://dd.weather.gc.ca/today/citypage_weather/ON/12/20250623T120424.641Z_MSC_CitypageWeather_s0000458_en.xml"

Bugs fixed

Prevent "Weather not available" error in some specific cases and locations

BEFORE	AFTER

Proposing to cherry-pick to 6.4.