Fix for chat prefix/suffix handling and mention pattern issue

[DimaSergeew]

We encountered an issue where the chat prefixes and suffixes were not displaying correctly due to an invalid regular expression in the mention pattern. The error in the logs was a PatternSyntaxException caused by an unclosed group.

Steps Taken:

Fixed the pattern handling to properly escape special characters in the player's display name.
Updated the mentions.pattern configuration to avoid unclosed groups and ensure compatibility with the regex engine.
Code Fix: In the MentionsTransformStrategy class, modify the patternForPlayer method to properly escape player names in the regex pattern:

private Pattern patternForPlayer(Player player) {
    try {
        // Escape special regex characters in the player's display name
        String escapedUsername = Pattern.quote(player.getDisplayName());
        return playerPatternCache.get(player, () ->
                Pattern.compile(settingsConfig.getMentions().getPattern().replace("{username}", escapedUsername)));
    } catch (ExecutionException e) {
        throw new IllegalStateException("Cannot compile mention pattern", e);
    }
}

This fix ensures that the player's display name is safely inserted into the regular expression without causing syntax errors.

Additional Information: After modifying the pattern handling, the chat now displays prefixes and suffixes correctly, and mentions are processed as expected.