Unify structure for ext/random's randomizer tests (#9410)

* Unify structure for ext/random's engine tests (2)

This makes adjustments that were missed in
2d6a883b3a1e5ee4f225dce6

Unify structure for ext/random's randomizer tests (#9410)

* Unify structure for ext/random's engine tests (2)

This makes adjustments that were missed in
2d6a883b3a1e5ee4f225dce64584ad2522e8e391.

* Add `engines.inc` for ext/random tests

* Unify structure for ext/random's randomizer tests

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Unify structure for ext/random's engine tests (#9321)

* Remove user_xoshiro128plusplus.phpt

This test does not exercise any of the code paths of the random extension and
thus is

Unify structure for ext/random's engine tests (#9321)

* Remove user_xoshiro128plusplus.phpt

This test does not exercise any of the code paths of the random extension and
thus is no value-add.

* Unify structure for ext/random's engine tests

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PcgOneseq128XslRr64::jump(): Throw ValueError for negative $advance (#9213)

* PCG64: $advance must be non-negative

Closes GH-9212