Allow specifying type-safe meta values

[matthewjamesadam]

Description

The @hey-api/sdk plugin generates a meta field on Options hardcoded to
Record<string, unknown>, which can be used as a side-channel for data to
interceptors/middleware. However this value is in effect untyped which can lead to
bugs:

await getFoo({ meta: { retryy: false } }); // typo'd key — compiles
await getFoo({ meta: { timeout: '30s' } }); // wrong type — compiles

This issue has been previously reported here: #2425 (comment)

I have a PR with a proposed solution here: #3996

[pullfrog]

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