feat: modify cache type to allow generic usage

[eungwang1]

Current Issue:
The current implementation of cache.get does not support explicit type definitions, which limits type safety and can lead to potential issues with type inference. Here's how it's currently implemented:

const { cache } = useSWRConfig();
const data = cache.get('key'); 

Proposed Changes:
This pull request modifies cache.get to accept generic type parameters, enhancing type safety by allowing developers to specify the expected return type. The modified implementation is as follows:

const { cache } = useSWRConfig();
const data = cache.get<KeyType>('key');

This update ensures better type checking and integration with TypeScript projects, aligning with modern development practices in type-safe applications.

[codesandbox-ci]

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