lru: consolidate LRU for go 1.20+

With Go 1.20+, interface-types become capable of satisfying comparable
constraints (with a runtime-check/panic). Thus it becomes possible to
deduplicate the two public types in the lru package.

Use build-tags to preserve compatibility with versions below go 1.20 by
preserving the legacy implementation.

go.mod

@@ -1,6 +1,6 @@
 module github.com/vimeo/galaxycache
 
-go 1.18
+go 1.20
 
 require (
 	github.com/golang/protobuf v1.4.3

lru/lru.go

@@ -1,3 +1,5 @@
+//go:build !go1.20
+
 /*
 Copyright 2013 Google Inc.
 

lru/lru_go120.go

@@ -0,0 +1,34 @@
+//go:build go1.20
+
+/*
+Copyright 2023 Vimeo Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package lru implements an LRU cache.
+package lru
+
+// A Key may be any value that is comparable. See http://golang.org/ref/spec#Comparison_operators
+type Key interface{}
+
+// Cache is an LRU cache. It is not safe for concurrent access.
+// This is a compatibility alias for TypedCache[Key,any]
+type Cache = TypedCache[Key, any]
+
+// New creates a new Cache.
+// If maxEntries is zero, the cache has no limit and it's assumed
+// that eviction is done by the caller.
+func New(maxEntries int) *Cache {
+	return TypedNew[Key, any](maxEntries)
+}