fix(logger): correctly pick powertools or custom handler in custom environments

[heitorlessa]

Issue number: #4277

Summary

This PR fixes a bug when a compute environment or customer preconfigures a standard logging logger with the same Powertools logger name.

Previously, we'd always pick the first handler - child or parent. However, it led to pick the incorrect one if a logger we're creating for the first time (Logger) was already pre-setup through other means (logging.getLogger).

import logging
import os

from aws_lambda_powertools import Logger

service_name = os.getenv("POWERTOOLS_SERVICE_NAME")

# A environment, third-party library, or customer intentionally creates a logger with the same name as Powertools
# and add a Handler

logging.getLogger(service_name).addHandler(logging.StreamHandler())

logger = Logger(service=service_name)  # Powertools will ask standard logging to give the previously setup logger, then configure another handler etc as expected 

Changes

Please provide a summary of what's being changed

• Encapsulate handler selection in _get_handler
• Reverse depend registered_handler on _get_handler
• Logger with two handlers and log items use both of them
• The above with a child logger
• Add explicit test for orphaned child without handler that will fail with AttributeError
• Create a backwards compatible exception to provide actionable error on orphaned child formatter (e.g., child init before parent and append_keys)
• Update docs to clarify child logger and their caveats

User experience

Please share what the user experience looks like before and after this change

Checklist

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• Meet tenets criteria
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented
• PR title follows conventional commit semantics

Is this a breaking change?

RFC issue number:

Checklist:

• Migration process documented
• Implement warnings (if it can live side by side)

Acknowledgment

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[leandrodamascena]

Hey @heitorlessa! I've pushed a commit with two small things, but this LGTM! Congrats for this great catch and fix.

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