feat: add bounded cache for opaque tokenizer only for last observed at cache (#9581)

Move away from unbounded cache for `lastObservedAt` stat, which was powered by BigCache (unbounded), to Ristretto, a bounded in-memory cache (https://github.com/dgraph-io/ristretto).

This PR is first step towards moving away from unbounded caches in the system, more PRs to follow.

go.mod

@@ -9,11 +9,11 @@ require (
 	github.com/DATA-DOG/go-sqlmock v1.5.2
 	github.com/SigNoz/govaluate v0.0.0-20240203125216-988004ccc7fd
 	github.com/SigNoz/signoz-otel-collector v0.129.4
-	github.com/allegro/bigcache/v3 v3.1.0
 	github.com/antlr4-go/antlr/v4 v4.13.1
 	github.com/antonmedv/expr v1.15.3
 	github.com/cespare/xxhash/v2 v2.3.0
 	github.com/coreos/go-oidc/v3 v3.14.1
+	github.com/dgraph-io/ristretto/v2 v2.3.0
 	github.com/dustin/go-humanize v1.0.1
 	github.com/go-co-op/gocron v1.30.1
 	github.com/go-openapi/runtime v0.28.0