refactor!: Rename GeocodioClient to Geocodio

[MiniCodeMonkey]

Summary

This PR renames the main client class from GeocodioClient to Geocodio for improved simplicity and consistency with other Geocodio SDKs.

Changes

• Renamed GeocodioClient class to Geocodio in src/geocodio/client.py
• Updated package exports in src/geocodio/__init__.py
• Updated all test files to use the new class name
• Updated README documentation and code examples
• Updated smoke test scripts

Breaking Change

⚠️ This is a breaking change - Users will need to update their imports:

# Old
from geocodio import GeocodioClient
client = GeocodioClient(api_key="...")

# New
from geocodio import Geocodio
client = Geocodio(api_key="...")

Test Plan

• Unit tests pass (53 tests passing)
• Import verification successful
• Test coverage maintained at 87%

Test Suites Covered:

• test_client.py - Client initialization and configuration tests
• test_geocoding.py - Geocoding functionality tests
• test_geocode.py - Geocode operation tests
• test_reverse.py - Reverse geocoding tests
• test_models.py - Data model tests
• test_exceptions.py - Exception handling tests
• test_errors.py - Error mapping tests