fix(core): throw when importing twice

[wmertens]

this should make it easier to detect build misconfigurations

Closes #3883

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[gioboa]

it looks great to me @wmertens 🤖

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commit: 32eb2be

[gioboa]

docs dev is not working

[shairez]

@wmertens summary of our meeting:

• Moving it to v2 instead of v1
• Enhancing the error message to provide a more thorough solution

Thanks!