Cross-runtime consistency fixes

Compare contract_event_handler.py, contract_status_changed_event_handler.py, and publication_evaluation_event_handler.py with the Java, TypeScript, and .NET runtimes. Review the listed timestamp, DynamoDB, environment-variable, validation, and metric behaviors first, then run the relevant service tests if available. Done means the Python handlers match the stated cross-runtime contracts without unintended writes or duplicate metrics.

Summary

A set of fixes to align the Python runtime with the other runtimes (Java, TypeScript, .NET) for functional equivalence and cross-runtime consistency.

Contracts Service

Timestamp format (contract_event_handler.py)

• create_contract: replaced datetime.now().strftime("%d/%m/%Y %H:%M:%S") with datetime.now(timezone.utc).isoformat() for both contract_created and contract_last_modified_on
• update_contract: replaced datetime.now().strftime(...) with datetime.now(timezone.utc).isoformat()
• Format change: custom DD/MM/YYYY HH:MM:SS → ISO 8601 YYYY-MM-DDTHH:MM:SS.ffffff+00:00
• Uses the non-deprecated timezone-aware API (timezone.utc) instead of datetime.utcnow()

DynamoDB attribute name (contract_event_handler.py)

• update_contract: changed UpdateExpression from "set contract_status=:t, modified_date=:m" to "set contract_status=:t, contract_last_modified_on=:m"
• This corrects a bug where update_contract wrote to a non-existent modified_date attribute instead of the correct contract_last_modified_on attribute used in create_contract

Observability metrics (contract_event_handler.py)

• Added metrics.add_metric(name="ContractCreated", unit=MetricUnit.Count, value=1) to create_contract success path

Approvals Service

Per-invocation timestamp (contract_status_changed_event_handler.py)

• Removed module-level now = datetime.now() and current_date variable assignments
• Moved timestamp computation inside the handler function body to ensure each invocation captures its own execution time rather than the container initialisation time

Environment variable error type (contract_status_changed_event_handler.py)

• Replaced raise InternalServerError(...) with raise EnvironmentError(...) for both SERVICE_NAMESPACE and CONTRACT_STATUS_TABLE missing variable checks
• Removed the now-unused InternalServerError import from aws_lambda_powertools.event_handler.exceptions

Web Service

Evaluation result validation (publication_evaluation_event_handler.py)

• Added validation guard: only updates DynamoDB when evaluation_result is "APPROVED" or "DECLINED" (case-insensitive)
• Logs a warning and returns without writing to DynamoDB for any other value

Metric name correction (publication_evaluation_event_handler.py)

• Removed duplicate metrics.add_metric(name="PropertiesAdded", ...) call
• Retained metrics.add_metric(name="PropertiesApproved", ...) as the single metric for this path