Lazy load bottom tabs

[jayohms]

Summary

By default, an app with bottom tabs loads every tab's initial screen at startup — each tab's navigator immediately visits its start location, even for tabs the user may never open. For apps with several tabs, this means a burst of web view visits up front.

This PR adds an opt-in that defers each tab's initial load until the tab is first selected. The initially selected tab still loads right away; the others load the first time you tap into them, and stay loaded afterward. This spreads out the work and avoids paying for tabs that are never visited.

Eager loading remains the default, so existing apps are unaffected unless they opt in.

Public API changes

HotwireBottomNavigationController gains a new optional constructor parameter, lazyLoadTabs: Boolean = false. Set it to true to enable deferred tab loading:

HotwireBottomNavigationController(
    activity = this,
    view = bottomNavigationView,
    lazyLoadTabs = true
)

No other public APIs change, and the default (false) preserves the current behavior.

Notes

• Deferral is scoped to bottom tab hosts only. Nested and standalone navigator hosts continue to load eagerly.
• The demo app enables lazyLoadTabs to exercise the new behavior.