[6.x] Fix infinite value for RedisStore

[driesvints]

This PR fixes storing infinite values for the Redis cache store. Since INF values will be converted to strings upon storing in Redis we'll need to serialize them.

Fixes #31345

[halaei]

That is fine for 6.x, except that you forget NAN.
For 7.x, type mismatches should also be handled, in a different PR.

[driesvints]

@halaei fixed NAN as well.

For 7.x, type mismatches should also be handled, in a different PR.

I don't know what you mean by this.

[halaei]

@driesvints

Cache::put('test', 1);
Cache::get('test'); // expected: integer 1, actual: string "1"

[driesvints]

@halaei not sure that's solvable tbh

[halaei]

@driesvints I think it is somehow solvable, even with no trouble for migration from 6.x to 7.x, except performance downsides for redis memory usage if someone is caching a lot of integer strings, e.g. "1" instead of 1.