Defer log record formatting until after filters

[happz]

Logger._log formatted the message - tmt run does not care, whatever is logged is also emitted and lands in log.txt, but there are commands that do not have log.txt, like tmt * ls, that do not have log file. Such commands could benefit from rendering of messages that would be actually emitted.

It turns out LogRecordDetails already contains everything we need to format the message. If the log record has details, we can easily postpone formatting.

Brief comparison of tmt test ls in tmt repo, on my workstation:

• before: 10 seconds (no prof), 25 seconds (with prof), 17/16/8 seconds in debug/_log/indent;
• after: 7 seconds (no prof), 17 seconds (with prof), 7/7 seconds in debug/_log, indent does not register.

Simple tmt in a repo with 179 plans takes 11 seconds before the change, 9 seconds after. In a repo with 3679 tests & 1 plan, 2 minutes 28 seconds before, 1 minute 33 seconds after.

The effect is measurable, reliably, running with profiler makes it stand out even more, yet it's not as big as expected.

PR addresses just one part of the formatting process, i.e. rendering of a message by logging subsystem from key and optional value fields, and its indentation. It does not address messages that are actually formatted in place, as f-strings, and never emitted. To address these, more work will be needed, as the next iteration on top of this PR.

Pull Request Checklist

• implement the feature
• write the documentation
• extend the test coverage
• update the specification
• adjust plugin docstring
• modify the json schema
• mention the version
• include a release note

[gemini-code-assist]

Code Review

This pull request introduces a custom LogRecord class and a type guard to handle custom log record details, refactoring formatting and filtering logic to use this custom record type. Feedback suggests chaining the log record factory instead of overriding it directly to preserve existing custom factories set by other libraries or test runners.

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[gemini-code-assist]

Chain the log record factory to preserve any existing custom factories set by other libraries or test runners. Overriding it directly can break logging capture or custom record types.

# Tell logging to use our custom log record class, preserving any existing factory.
_old_factory = logging.getLogRecordFactory()


def _log_record_factory(*args: Any, **kwargs: Any) -> logging.LogRecord:
    record = _old_factory(*args, **kwargs)
    if not isinstance(record, LogRecord):
        record.__class__ = LogRecord
    return record


logging.setLogRecordFactory(_log_record_factory)