Add caching for PriceReader

[0xnogo]

We are currently making many RPC calls to get token prices, which can slow down our system. This PR introduces a simple caching solution to store and reuse these values.

Changes made:

• Added caching to store fetched token prices in PriceReader
• Split price fetching logic into smaller functions
• Used "never expire" policy since we refresh prices each time

The implementation wraps go-cache and can be extended for other use cases. It supports:

• Basic cache operations (Get/Set/Delete)
• Custom eviction functions
• Thread-safe operations
• Generic value types

[dimkouv]

i believe it can be just inMemCache no need to tie it to decimals

[0xnogo]

It depends if we have more than one cache. I'll leave it as-is for now and potentially update the name if this is the only cache of the class. wdyt?

[winder]

What about an off the shelf library?
https://github.com/eko/gocache
https://github.com/allegro/bigcache
https://github.com/dgraph-io/ristretto
https://github.com/patrickmn/go-cache

[0xnogo]

I checked the libs you provided and they look quite advanced. I'm not sure about our future requirements but our current needs are quite simple. It might makes sense to go homemade for our usecase.

Do you have any experience with those libs? What do you recommend?

[winder]

I almost used ristretto for a project that needed high performance, but you're probably right that it's excessive for our needs.

Two trains of thought right now:

1. go-cache seems like an excellent fit. It's extremely lightweight (a single file with ~1000 LOC), the interface is almost identical to the one you have, the project has the most stars.

2. If we do roll our own, I bet we could come up with a clever optimization to time based expiration utilizing sequence numbers and multiple maps.

[0xnogo]

We can go with a with go-cache and overload it with a custom logic to implement the customPolicy. Something like this:

type CustomCache[K comparable, V any] struct {
	cache        *cache.Cache
	customPolicy func(V) bool
	mutex        sync.RWMutex
}

func (c *CustomCache[K, V]) Get(key K) (V, bool) {
	c.mutex.RLock()
	defer c.mutex.RUnlock()

        ...

	// Check custom policy
	if c.customPolicy != nil && c.customPolicy(typedValue) {
		c.cache.Delete(interface{}(key))
		return zero, false
	}

	return typedValue, true
}

[asoliman92]

I'd like to see tests for the time based eviction with one test that is skipped with a TODO to make a proper background task to evict.

[github-actions]

Metric	ng/cache-decimals	main
Coverage	77.1%	76.4%