Add type hints to private properties #1102

Job	Run time
PHP 8.2	13s
PHP 8.3	18s
extra/cache-extra with PHP 8.2	14s
Integration tests with PHP 8.2	50s
extra/cssinliner-extra with PHP 8.2	20s
extra/html-extra with PHP 8.2	14s
extra/inky-extra with PHP 8.2	15s
extra/intl-extra with PHP 8.2	23s
extra/markdown-extra with PHP 8.2	14s
extra/string-extra with PHP 8.2	51s
extra/twig-extra-bundle with PHP 8.2	25s
extra/cache-extra with PHP 8.3	15s
extra/cssinliner-extra with PHP 8.3	20s
extra/html-extra with PHP 8.3	14s
extra/inky-extra with PHP 8.3	13s
extra/intl-extra with PHP 8.3	15s
extra/markdown-extra with PHP 8.3	13s
extra/string-extra with PHP 8.3	13s
extra/twig-extra-bundle with PHP 8.3	24s
	6m 24s

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