Support for a Counter-caching API

[Turnerj]

Similar to discussions in dotnet/extensions#709 & stefanprodan/AspNetCoreRateLimit#83, add support for a new counter cache stack. This is a unique cache stack type with atomic actions by design.

public interface ICounterCacheStack<TContext>
{
    ValueTask<long> GetAsync(string cacheKey);
    ValueTask SetAsync(string cacheKey, long value, CacheSettings settings);
    ValueTask<long> IncrementAsync(string cacheKey, CacheSettings settings);
    ValueTask<long> DecrementAsync(string cacheKey, CacheSettings settings);
    ValueTask<long> IncrementByAsync(string cacheKey, long value, CacheSettings settings);
    ValueTask<long> DecrementByAsync(string cacheKey, long value, CacheSettings settings);
}

Providers:

• In-memory: Need to research atomic operations for memory storage
• Redis: INCR, INCRBY, DECR & DECRBY. May need to even go further and use Lua scripts in Redis like this example.
• MongoDB: Should be possible with custom commands though not sure if it is even necessary. MongoDB would likely never perform fast enough to be used in this manner.

Other thoughts:

• Still likely need to support auto-evicting etc, at least for the in-memory version. That is unless this new cache stack type has a custom memory provider different from the main one.
• Do I need to support remote evicting too (provided through my Redis extension)?
• Does this actually need a TContext?

[Turnerj]

Thinking about this a little more, I'd probably go down the path of splitting cache layers into categories like:

• Common (This is what already exists)
• Counters (This is what this issue proposes)
• ... (Anything else that may come up later)

Rather than try and squish everything into a single stack and provider, basically have interfaces and providers for each specific "category". Its not like DB or Disk caching would be a high priority for counters but are of reasonable importance for "common" caching.

[Turnerj]

This is still conceptually interesting but deviates from the main goal of the library too much in my opinion, making it harder to maintain the library in the future.