PercentFormatterStyle._format() now performs %(key)s/d/f substitution
against LogRecord attributes. Formatter.format() sets record.message
via getMessage() and conditionally calls formatTime() for asctime.
formatTime() uses JS Date with strftime-style tokens (%Y,%m,%d,%H,
%M,%S) or ISO8601 fallback. formatError() returns Error.stack.
BASIC_FORMAT updated to use %(levelname)s. Fixed datefmt type in
config.ts.
Add format() method to Formatter class to delegate to the style's
format method. Change Placeholder.loggers to public so Manager can
access it for hierarchy fixup.
