Add `SystemIdTemplate` to allow one-shot system in bsn!#24026

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hxYuki wants to merge 9 commits intobevyengine:mainfrom

hxYuki:system-id-template

Commits on Apr 29, 2026

mvp

hxYuki
and
Copilot
committed

Commits on Apr 30, 2026

fix clone

hxYuki
and
Copilot
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the way you use an `Arc`
hxYuki
committed
try use relations to handle `SystemId` reference
hxYuki
committed

Commits on May 3, 2026

handle system unregistering & prevent multiple registration
hxYuki
committed

Commits on May 4, 2026