feat(useStorage): add waitOnMounted option for SSR

[posva]

Close #3447

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🤖 Generated by Copilot at a84b5c3

Added a waitOnMounted option to useStorage to improve SSR compatibility. Updated the test file to cover the new option.

🤖 Generated by Copilot at a84b5c3

• Add waitOnMounted option to useStorage function to delay reading the storage value until the component is mounted (link, link, link)
• Import tryOnMounted helper from @vueuse/shared to implement the deferred update logic in useStorage (link)
• Add test case for waitOnMounted option in useStorage/index.test.ts, using defineComponent, nextTick, and mount from vue-test-utils (link, link)

[posva]

BTW: I think it’s worth checking with an native English speaker if the option name sounds good

[antfu]

Maybe readOnMounted or initOnMounted? To me, it's a bit unclear what to "wait" on

[posva]

Sounds good to me!