Add FMI weather provider

[i-xul]

Description

This pull request adds the Finnish Meteorological Institute (FMI) as a weather provider for the default weather module.

The provider uses FMI Open Data services and does not require an API key.

It supports:

• Current weather observations from FMI weather stations
• Automatic selection of the nearest station with the required observations
• Hourly forecasts using the FMI HARMONIE model
• Daily forecasts aggregated from HARMONIE forecast data
• Finnish local calendar days for daily forecast aggregation
• FMI weather symbol mapping to MagicMirror weather types
• Temperature, humidity, wind, precipitation, and related weather data

The implementation uses latitude and longitude coordinates, consistent with the existing weather provider configuration.

Related issue

No related issue.

Additional changes

• Adds FMI-specific unit tests covering configuration, URL construction, observation parsing, station selection, current weather generation, forecast parsing, hourly forecasts, daily forecasts, and forecast fetching.
• Extends the HTTP fetcher to support the FMI XML responses required by the provider.
• Adds tests for the HTTP fetcher changes.
• Adds FMI-related terms to the spelling dictionary.
• Adds FMI to the weather provider release-note category.

Testing

Tested locally on Windows 11.

FMI provider tests:

17 passed (17)

Full unit test suite:

489 passed, 1 failed (490 total)

The single failing test is tests/unit/classes/systeminformation_spec.js, which expects platform: linux. The local test environment reports platform: Windows. The FMI provider tests pass successfully.

npm run config:check also passes successfully.

The provider was additionally tested with live FMI data in MagicMirror using current, forecast, and hourly weather module instances.

[KristjanESPERANTO]

Thanks for the PR! This looks good overall, except the url usage.

I see potential to consolidate things, since we have some similarities with the provider evcanada. I'd probably address that in a follow-up PR.

[KristjanESPERANTO]

@i-xul Can you please also add FMI to the docs? :)

https://github.com/MagicMirrorOrg/MagicMirror-Documentation/blob/master/modules/weather.md#general-options