Fix issue 19525 - Duration is not usable with zero-arg std.algorithm.sum

[Biotronic]

This teaches sum to look for Seed.zero if no constructor taking an int is found for the type.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	19525	enhancement	Duration is not usable with zero-arg std.algorithm.sum

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + phobos#7504"

[wilzbach]

Thanks!