[nazirgitwork]

Summary

KbqTreeSelection did work proportional to the number of rows several times on each render, and some of it for each row. In a large tree that work grew with the square of the number of rows. This PR removes the quadratic paths and the per-row subscriptions. It also stops mouseenter from running change detection in trees outside a select.

List of notable changes:

• updated the option ordering in KbqTreeSelection: options are indexed once into a by-node map and a by-value map. Before, unorderedOptions was searched for every node, which was O(n²). As before, the first option wins in each map, and a node match takes precedence over a value match.
• updated optionFocusChanges / optionBlurChanges: each one is now a single stream that options report to through the new KbqTreeOptionParent.reportOptionFocus() / reportOptionBlur() methods. Before, every call merged the streams of all rendered options, and the tree re-subscribed after each render. That cost O(n) per render, and a subscriber never received focus events from rows rendered after it subscribed. It now does.
• fixed the focus of a row that a data change brings in: it reaches the key manager immediately. Before, the per-option subscriptions were only rebuilt after delay(0), so a row focused in that gap was missed.
• updated KbqTreeOption: mouseenter is no longer a host listener. It is bound outside the Angular zone and re-enters the zone only when the tree is inside a select, the only case that reacts to it. A tree outside a select no longer checks views for every row the pointer crosses.
• added tests: no view checks on mouseenter outside a select, focus of a newly rendered row, optionFocusChanges reporting rows rendered after subscribing, and keyboard order across expand, collapse and new data when rows share values.
• updated the API golden file and the check-api-docs baseline: two new members, and optionFocusChanges / optionBlurChanges are now documented.

What should reviewers focus on?

• KbqTreeOptionParent gains two required methods. Code that provides its own implementation of KBQ_TREE_OPTION_PARENT_COMPONENT will stop compiling until it adds them. Is that acceptable here, or should they be optional?
• optionFocusChanges / optionBlurChanges now also emit for rows rendered after the subscription. Before, the observable covered only the rows rendered when the getter was called.
• The mouseenter listener runs outside the zone. Please check it in zoneless apps and in kbq-tree-select, where hovering a row still has to move focus.