Improve performance and country picker customization (#876)

* Add background data loading and cell customization

* Fix sectionIndexTitles

* Add automatic show/hide keyboard on opening/closing country picker

* Add PhoneNumberTextFieldDelegate

* Fix UINavigationBarDelegate implementation

* Add Test project with custom header/cell views

* Enhancements for iOS 26

* Fix hostNavigationControllerDelegate handling

* Fix hostNavigationControllerDelegate handling

* Add default implementation for PhoneNumberTextFieldDelegate

* Fix hostNavigationControllerDelegate handling

* Allow to subclass TextField and apply additional configs

* Update README

Release 4.1.10

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Release 4.1.3

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Release 4.1.1

Release 4.1.0