Feature: Add FMI Open Data WFS station metadata parser

[lkananen]

I have added the support for station metadata API endpoint (fmi::ef::stations) and functionality to download_and_parse that data.

Changes:

• station.py file added. Implements download_and_parse for the stations.
• test_station.py file added. Test the station.py implementation.
• wfs.py updated to included necessary XML Elements used by station.py.
• README.MD section added for stations. Examples included there.

[lkananen]

AI generated detailed description of the full list of changes below:

Core Implementation (station.py):

• Implement Station class to parse EnvironmentalMonitoringFacility XML
• Extract station metadata: FMISID, name, coordinates, region, country
• Support multiple network types per station (station_type as list)
• Add INSPIRE ID fields (local_id, namespace)
• Include measurement regime and mobile_status fields
• Provide helper methods for filtering stations by:
  • ID, name, type, region, and country

Test Suite (test_station.py):

• Add 30+ comprehensive test cases achieving 90%+ code coverage
• Three test classes: TestStationParser, TestStationValues, TestStationErrorCases
• Cover parsing, data validation, helper methods, and error handling
• Validate field formats (coordinates, WMO IDs, INSPIRE IDs, timestamps)
• Test multiple station types and data consistency

Infrastructure Updates:

• Update wfs.py with station-related XML tag constants:
  • EF_* constants for Environmental Monitoring Facilities
  • INS_BASE_* constants for INSPIRE identifiers
  • XLINK_TITLE for network type extraction
• Add station query handler to download_stored_query()

Documentation (README.md):

• Add comprehensive station metadata section with examples
• Document data structure with all 16 fields
• Provide usage examples for all helper methods
• Explain multiple network types support

Follows INSPIRE EF 4.0 schema for environmental monitoring facilities.

[lkananen]

Related stored query:
wfs.py: Environmental Monitoring Stations