Eliminate monitor update handling macros

Convert all monitor update handling macros to methods:
- handle_monitor_update_completion -> prepare_monitor_update_completion_data
- handle_initial_monitor -> method returning Option<MonitorUpdateCompletionData>
- handle_new_monitor_update -> method returning Option<MonitorUpdateCompletionData>
- handle_post_close_monitor_update -> method returning Option<Vec<MonitorUpdateCompletionAction>>

The new pattern at call sites is:
  if let Some(data) = self.handle_*_monitor_update(...) {
      mem::drop(locks);
      self.handle_monitor_update_completion_data(data);
  }

This eliminates macro complexity while maintaining the same lock-release
semantics required for correct monitor update handling.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: joostjager