Cleanup of IdeLogEntry, IdeLogListener and IdeGuiLogListener #2385

Task summary

This ticket collects the review suggestions from #2053 (review) that were not resolved before merging. Things to do:

1. IdeLogListener takes an IdeLogEntry as its only argument

• Change IdeLogListener.onLog(IdeLogLevel, String, String, Object[], Throwable) to boolean onLog(IdeLogEntry entry).
• Slf4jLoggerAdapter.handleNormalizedLoggingCall builds the IdeLogEntry once and passes it to the listener.
• Update all implementations: IdeLogListenerBuffer (adds the entry directly instead of creating a new one), IdeLogListenerNone, IdeGuiLogListener and IdeLogListenerCollector (test).
• Creating an IdeLogEntry for every log event costs very little, and the simpler API is worth it.

2. IdeLogEntry: timestamp as Instant

• Change the record component Long timeStamp to Instant timestamp and create it with Instant.now(). An Instant is readable in the debugger and in toString(), while a long is just a large number.
• In displayValue(), make the DateTimeFormatter a static final constant instead of creating it on every call. Use the Instant directly.
• Add the missing @param Javadoc for the timestamp.

3. IdeGuiLogListener: show each message only once

At the moment onLog ignores the return value of super.onLog(...) and always returns true. While the listener is buffering (the default after the constructor), a message:

• goes into the buffer and is still written to the GUI console at once,
• is passed on to the regular logger, even though buffering should suppress it,
• is written to the console a second time when the buffer is flushed.

Fix: only forward the message if the parent class accepts it:

boolean accept = super.onLog(entry);
if (accept && (this.consoleController != null)) {
  this.consoleController.appendOutput(entry);
}
return accept;

4. ConsoleController works with IdeLogEntry

• IdeGuiLogListener passes the whole IdeLogEntry to the controller. It no longer passes only level + message, and it no longer adds a separate line " Error: " + error.getMessage() at the hard-coded ERROR level.
• The controller stores the full entry, including error(), so the GUI can show the exception later.
• Check whether the convenience methods appendOutput(String) and appendOutput(IdeLogLevel, String) are still needed (they are used by GuiOutputListener, CommandletService and ConsolePanelTest).

Out of scope (follow-up ticket): In the console, mark entries that have an exception with an icon. Clicking the icon opens a popup with the full stack trace, which can be scrolled and has a "copy to clipboard" button. This ticket only has to make sure the API keeps the Throwable available for that.

Acceptance criteria

• IdeLogListener.onLog(IdeLogEntry) is the only listener method, and all implementations are migrated.
• IdeLogEntry uses Instant for the timestamp, and displayValue() uses a constant formatter.
• While buffering, a message logged in the GUI shows up exactly once in the console and is not passed on to the regular logger.
• ConsoleController receives and stores IdeLogEntry objects, including the error.
• Tests are adjusted or added, at least for the buffering case in IdeGuiLogListener.

Additional context

#2053