Add in-memory caching pkg

[ahrav]

• Define a cache interface along w/ an in-memory implementation.
• This will be used by the GCS source to track progress. It can also be used by any other source that needs progress tracking via a cache.
• Adding the interface abstraction allows us to implement other types of caches if needed.

caching library used -> https://pkg.go.dev/github.com/patrickmn/go-cache?utm_source=godoc

[mcastorina]

Very nice!

[mcastorina]

Suggestion (optional): If you do want to add convenience methods for actually serializing/deserializing the data, we could use strings.Replacer to escape commas (assuming it has an acceptable benchmark).

For example:

func unescape(s string) string {
	replacer := strings.NewReplacer(`\,`, ",")
	return replacer.Replace(s)
}

func escape(s string) string {
	replacer := strings.NewReplacer(",", `\,`)
	return replacer.Replace(s)
}