Added nothrow @nogc @safe to the allocate function.

[George-Alex-Berea]

Also added these flags to all the functons it calls.
In order to make the functions safe I isolated the 'unsafe' parts inside @trusted lambda expressions, inspired by edi33416's pull request #6416.
Additionally, added nothrow @nogc @safe to the allocateAll function, since it only calls allocate.

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[teodutu]

@edi33416 if you remember any of this from ages ago, please add your review as it revives your work.