Add `mixed` parameter and return types to `FilterInterface` #372

Job	Run time
ci / Generate job matrix	7s
ci / QA Checks (PHPUnit [8.1, locked], ubuntu-latest, laminas/laminas-continuous-integration-action@v1...	28s
ci / QA Checks (PHPUnit [8.1, lowest], ubuntu-latest, laminas/laminas-continuous-integration-action@v1...	26s
ci / QA Checks (PHPUnit [8.1, latest], ubuntu-latest, laminas/laminas-continuous-integration-action@v1...	31s
ci / QA Checks (PHPUnit [8.2, lowest], ubuntu-latest, laminas/laminas-continuous-integration-action@v1...	23s
ci / QA Checks (PHPUnit [8.2, latest], ubuntu-latest, laminas/laminas-continuous-integration-action@v1...	26s
ci / QA Checks (PHPCodeSniffer [8.1, locked], ubuntu-latest, laminas/laminas-continuous-integration-ac...	24s
ci / QA Checks (Psalm [8.1, locked], ubuntu-latest, laminas/laminas-continuous-integration-action@v1, ...	29s
	3m 14s

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