drop support of php73/74

[jkowalleck]

on 2022-11-28 the support for php7.4 ended.

lets take this for a change to switch the min-version of this lib to 8.0 .
see https://www.php.net/manual/en/migration80.new-features.php

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on 2021-12-06 the support for php7.3 ended.

lets take this for a change to switch the min-version of this lib to 7.4 .
see https://www.php.net/manual/en/migration74.new-features.php

so to use the new language features, a breaking change might happen.

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• drop php73/74 from CI
• drop php73/74 from composer manifest (php: ^8.0)
• update dev-tools to a version that does not need php73/74 - depeds on chore: add composer-normalize tool #29
• migrate to php80 via php-cs-fixer
• make class properties type-save
• TODO: gather additional list of changes to apply to the source code