Fix interactive resizing regression from Issue #536

[vincentarelbundock]

Fix #540

Problem

PR #438 fixed a long-standing issue where resizing the plot window
would cause legends to become misaligned. The fix worked by wrapping
coordinate-dependent calculations inside recordGraphics(), which R
replays when the device is resized.

PR #536 refactored the legend code but inadvertently broke this fix.
The refactoring moved critical calculations outside of
recordGraphics():

  # These now happen OUTSIDE recordGraphics - only run once at initial  
  size:                                                                 
  legend_outer_margins(legend_env, apply = draw)     # margin adjustment
  legend_env$inset = measure_legend_inset(legend_env) # inset           
  calculation                                                           
  plot.new()  # plot refresh                                            
                                                                        
  # INSIDE recordGraphics - only this replays on resize:                
  recordGraphics({                                                      
    do.call("legend", legend_env$args)  # draws with STALE inset values 
  }, ...)                                                               
                      

When the window is resized, only the final legend() call replays, but
it uses margin/inset values calculated for the original window size.

Fix

Move the margin application, inset calculation, and plot refresh back
inside recordGraphics() via a new tinylegend() helper function:

  # Initial setup only (first plot.new, measurement):                   
  legend_outer_margins(legend_env, apply = FALSE)                       
                                                                        
  # Store base values for replay:                                       
  legend_env$omar_base = legend_env$omar                                
  legend_env$ooma_base = legend_env$ooma                                
  legend_env$inset_base = legend_env$args[["inset"]]                    
                                                                        
  # Everything else inside recordGraphics:                              
  recordGraphics(                                                       
    tinylegend(legend_env),  # recalculates margins, inset, then draws  
    list = list(legend_env = legend_env),                               
    env = getNamespace("tinyplot")                                      
  )                                                                                                                              

The tinylegend() function resets to base values on each replay, then
recalculates soma, applies margins, calculates inset, and
draws—ensuring correct positioning after resize.

[vincentarelbundock]

Disclaimer: This solution was 1-shotted by Claude Code after I fed it .diff files for the two PRs mentioned above.

I have reviewed the code. The changes seem pretty straightforward and, AFAICT, "correct".

I have also tested it locally and resizing the Positron window no longer cuts-off the legend.

[grantmcdermott]

Code LGTM too. Local testing confirms the fix.

Thanks for the quick turnaround @vincentarelbundock (and Claude)!