Document Python best practices for arabesque-sray organisation

[Copilot]

Consolidates Python development standards from arabesque-sray/ops and arabesque-sray/esgbook-py into a single reference document.

What's Included

• Code style: 100-char line length, singular directory naming
• Project structure: Flat layout with hexagonal architecture (entity/, use_case/, service/, repository/)
• Data modeling: When to use standard dataclass vs Pydantic dataclass vs BaseModel vs BaseSettings
• Logging: structlog with JSON output for GCP, context binding patterns
• Tooling: uv package manager, ruff, mypy, pytest
• Custom libraries: esgbook-py modules (logging setup, retry configs, storage utilities)

Key Patterns

# Logging with context
from structlog.contextvars import bound_contextvars

logger = structlog.get_logger(__name__)

with bound_contextvars(request_id=req_id):
    logger.info("processing")  # automatically includes request_id

# Configuration
from pydantic_settings import BaseSettings
from pydantic import BaseModel

class DatabaseConfig(BaseModel):
    host: str
    port: int = 5432

class Settings(BaseSettings):
    database: DatabaseConfig
    
    model_config = SettingsConfigDict(
        env_file='.env',
        env_nested_delimiter='__'
    )

Document includes decision trees, code examples, and quick reference guides for common scenarios.

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