log: export public component flag filter for custom handlers

[rezib]

Summary

rfl.log.setup_logger and enforce_debug apply the same log_flags / debug_flags filter as a private nested function. Callers that attach extra root handlers (OTLP bridges, custom stream handlers, etc.) cannot reuse that logic without copying it.

Please export a small public helper that implements the same semantics, and use it inside RFL.

Current behavior

Flag filtering is inlined in both setup_logger and enforce_debug, roughly:

def custom_filter(record):
    component = record.name.split(".")[0]
    if record.levelno == logging.DEBUG:
        if "ALL" in debug_flags or component in debug_flags:
            return 1
        return 0
    if "ALL" in log_flags or component in log_flags:
        return 1
    return 0

It is not in __all__ and not reusable for handlers RFL does not create.

Motivation

Consumers already reimplement this as a local component_flag_filter so that:

• an OTLP LoggingHandler applies the same allow-list as stream logging
• a future dual stdout/stderr setup (see log: split streams so levels below WARNING go to stdout #98) can attach the same filter to both handlers without depending on setup_logger internals

Duplicating ~15 lines is fine short-term, but semantics can drift if RFL ever changes flag rules (ALL, first segment of record.name, DEBUG vs non-DEBUG lists).

Proposed API

Something like:

def component_flag_filter(
    log_flags: list[str] | None = None,
    debug_flags: list[str] | None = None,
) -> logging.Filter | Callable[[logging.LogRecord], bool]:
    ...

Requirements:

• Same semantics as today’s nested filter (ALL, logger name first segment, DEBUG gated by debug_flags only)
• Used internally by setup_logger and enforce_debug (single implementation)
• Documented and exported from rfl.log (__all__)

Exact return type (Filter subclass vs callable) is up to maintainers; a callable compatible with Handler.addFilter is enough.