Fix/column reordering reactive preferences

[johanrd]

Summary

Makes ColumnReordering react to restored preferences, matching ColumnVisibility behavior.

Problem

ColumnReordering read preferences only once at construction:

columnOrder = new ColumnOrder({                                                                                                                                                                                                                                                                       
  existingOrder: this.read(),  // ← Called once, never again                                                                                                                                                                                                                                          
});                                                                                                                                                                                                                                                                                                   

When preferences were restored (e.g., from an API), ColumnVisibility would update but ColumnReordering would not.

Solution

Add a read callback that's called reactively:

columnOrder = new ColumnOrder({                                                                                                                                                                                                                                                                       
  read: () => this.read(),  // ← Called each time orderedMap is accessed                                                                                                                                                                                                                              
});  

The orderedMap getter now prefers the read() result (from preferences) over the local map, making it reactive to preference changes.

Builds upon #149, which can be closed if this is merged.

• Use TrackedMap for plugins and columns containers so restore() triggers tracking
• Add non-mutating getters (getPlugin, getColumn) to avoid "mutation during render" errors

Test plan

• New test: "ColumnReordering reacts to restored preferences"
• Verified test fails before fix, passes after
• All 185 tests pass (with tracked builtins 4.0.0 override)

[NullVoxPopuli]

can you rebase this one?

[johanrd]

@NullVoxPopuli done!

Side note: I was also thinking to explore if the preferences arg to headlessTable could accept a thunk (for reactive puprposes), where multiple tables on the same view should react to the same preferences adapter. Maybe niche – but maybe you have thoughts?

[NullVoxPopuli]

seems like a fine overload to support

[johanrd]

thanks, see #156