Assuming a %stats hash has been declared, the File::Find callback can be as simple as:

sub wanted {
    return unless -f;
    /(?<!^)[.]([^.]+)$/;
    ++$stats{$File::Find::dir}{$1 || ''};
}
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That will cause all files without an extension, as well as hidden files without an extension (e.g. .bashrc), to be counted together under a '' key. Everything else will counted under keys without a leading '.', e.g. 'pl', 'txt', 'png', etc.

If counts for individual directories aren't required, that can be simplified even further by just using:

++$stats{$1 || ''};
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