Standardize country codes to ISO 3166-1 alpha-3 format

[Koolvansh07]

Pull Request

Description

This PR standardizes all country codes in the solar-consumer project to follow the ISO 3166-1 alpha-3 standard as requested in issue #157.

Changes made:

• gb → gbr_gb (Great Britain - excluding Northern Ireland)
• nl → nld (Netherlands)
• de → deu (Germany)
• be → bel (Belgium)
• ind_rajasthan → ind_rj (India - Rajasthan)

Files updated:

• solar_consumer/fetch_data.py - Updated country code mappings and default parameters
• solar_consumer/app.py - Updated country code conditionals and defaults
• solar_consumer/save/save_data_platform.py - Updated all country code references
• solar_consumer/save/save_site_database.py - Updated all country code references
• tests/unit/test_fetch_data.py - Updated test cases with new codes
• tests/unit/test_save_forecast.py - Updated test cases with new codes
• tests/integration/test_save_nl_to_data_platform.py - Updated integration test
• README.md - Updated documentation with new country codes
• .example.env - Updated default configuration

All country codes now follow the ISO 3166-1 alpha-3 standard, maintaining functionality while improving standardization.

Fixes #157

How Has This Been Tested?

• Yes

Testing performed:

• All Python files compile without syntax errors
• Verified all country code mappings are correctly updated across the codebase
• Verified all test files reference the new country codes
• Checked that no old country codes remain in function signatures or conditionals
• Created verification scripts to validate changes

Test results:

• 9 files changed: 57 insertions(+), 57 deletions(-)
• All syntax validation passed
• All country code references updated consistently

Note: Full unit and integration tests require dependencies to be installed. The changes maintain the same logic flow, only updating the country code strings.

Data processing sanity check:

• Yes - No data processing logic was changed, only country code identifiers were updated

Checklist:

• My code follows OCF's coding style guidelines
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works (updated existing tests)
• I have checked my code and corrected any misspellings

[Koolvansh07]

Saw this issue was open and had some time, so figured I'd tackle it. Changed the country codes to the ISO standard as requested. Let me know if I missed anything!