fix: prevent cache size underflow

[acha-bill]

Checklist

• I have read the coding guide.
• My change requires a documentation update, and I have done it.
• I have added tests to cover my changes.
• I have filled out the description and linked the related issues.

Description

Prevent cache size from underflowing

Open API Spec Version Changes (if applicable)

Motivation and Context (Optional)

Related Issue (Optional)

#4982

Screenshots (if appropriate):

[istae]

Has the underflow happened in production?

[gacevicljubisa]

Size filed is of type Int64, so negative number are allowed.

type Cache struct {
	size     atomic.Int64
	capacity int
	glock    *multex.Multex // blocks Get and Put ops while shallow copy is running.
}

[acha-bill]

Has the underflow happened in production?

Only mentioned in #4982

Size filed is of type Int64, so negative number are allowed.

But when returning, it's cast to uint64. This causes the underflow to MaxUint64 if size was < 0

[gacevicljubisa]

Has the underflow happened in production?

Only mentioned in #4982

Size filed is of type Int64, so negative number are allowed.

But when returning, it's cast to uint64. This causes the underflow to MaxUint64 if size was < 0

Then we should return error if size is 0 or less, right? Is it allowed to be 0 or less and in which cases?