fix(logger): fix exception on flush without buffer

[tonnico]

Issue number: #6793

Summary

Changes

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earlier exit when no buffer config is set.

User experience

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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)

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 96.21%. Comparing base (a5482c8) to head (aaca9de).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
aws_lambda_powertools/logging/logger.py	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #6794   +/-   ##
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  Coverage    96.21%   96.21%           
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  Files          273      273           
  Lines        12691    12691           
  Branches       946      946           
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  Hits         12211    12211           
  Misses         375      375           
  Partials       105      105           

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[leandrodamascena]

Hey @tonnico thanks for sending this PR. Your fork doesn't allow modification, so, can you please add this test to make sure we are testing this situation?

File: https://github.com/tonnico/powertools-lambda-python/blob/c2dd26f297cfcb8834cc0ecd96f256259a5acd9d/tests/functional/logger/required_dependencies/test_powertools_logger_buffer.py

def test_flush_buffer_without_buffer_config(stdout, service_name, lambda_context, monkeypatch):
    # Set initial trace ID for first Lambda invocation
    monkeypatch.setenv(constants.XRAY_TRACE_ID_ENV, "1-67c39786-5908a82a246fb67f3089263f")

    # GIVEN A logger without buffer configuration
    logger = Logger(level="DEBUG", service=service_name, stream=stdout)

    @logger.inject_lambda_context(flush_buffer_on_uncaught_error=True)
    def handler(event, context):
        # Log messages that should be flushed when an exception occurs
        logger.debug("this log line will be flushed after error - 1")
        logger.debug("this log line will be flushed after error - 2")
        raise ValueError("Test error")

    # WHEN Invoking the handler and expecting a ValueError
    # AND flush_buffer_on_uncaught_error is True but there is no logger buffer configuration
    with pytest.raises(ValueError):
        handler({}, lambda_context)

    # THEN Verify that buffered log messages are flushed without any exception
    log = capture_multiple_logging_statements_output(stdout)
    assert len(log) == 2, "Expected two log messages to be flushed"