Avoid array-to-string and null replacement warnings in PrettyBlocks and shortcodes

[CySSoO]

Motivation

• Prevent PHP warnings like "Array to string conversion" when PrettyBlocks labels are arrays and avoid deprecation notices when null is passed to str_replace during shortcode/template rendering.

Description

• In src/Service/EverblockPrettyBlocks.php guard label extraction by normalizing the $config[$labelField] value: if it's an array use the first element, and only cast scalar values to string before using as a label.
• In src/Service/EverblockTools.php ensure replacements never pass non-scalar or null directly to str_replace by coercing values to safe strings in renderSmartyVarsInArray, getCustomerShortcodes, and getEverShortcodes.
• These changes avoid array-to-string casts and deprecated null replacements while preserving existing fallback behavior.

Testing

• No automated tests were run for this change.

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Codex Task