PHP 8.2: Deprecated: Creation of dynamic property

[joshuafredrickson]

Describe the bug
Running PHP 8.2 receives the following deprecation warnings:

Deprecated: Creation of dynamic property ResponsivePicsWP::$api is deprecated in /***/wp-content/plugins/responsive-pics/src/class-responsive-pics.php on line 102
Deprecated: Creation of dynamic property ResponsivePicsWP::$helpers is deprecated in /***/wp-content/plugins/responsive-pics/src/class-responsive-pics.php on line 103
Deprecated: Creation of dynamic property ResponsivePicsWP::$error is deprecated in /***/wp-content/plugins/responsive-pics/src/class-responsive-pics.php on line 104
Deprecated: Creation of dynamic property ResponsivePicsWP::$process is deprecated in /***/wp-content/plugins/responsive-pics/src/class-responsive-pics.php on line 105
Deprecated: Creation of dynamic property ResponsivePicsWP::$rules is deprecated in /***/wp-content/plugins/responsive-pics/src/class-responsive-pics.php on line 106
Deprecated: Creation of dynamic property ResponsivePicsWP::$breakpoints is deprecated in /***/wp-content/plugins/responsive-pics/src/class-responsive-pics.php on line 107
Deprecated: Creation of dynamic property ResponsivePicsWP::$grid is deprecated in /***/wp-content/plugins/responsive-pics/src/class-responsive-pics.php on line 108
Deprecated: Creation of dynamic property ResponsivePicsWP::$sources is deprecated in /***/wp-content/plugins/responsive-pics/src/class-responsive-pics.php on line 109

Expected behavior
Fewer deprecation warnings in PHP 8.2 ;)

Software (please complete the following information):

• PHP Version: 8.2.x
• ResponsivePicture version: 1.7.5