refactor: encapsulate cache as decorator

[mweberxyz]

In preparation for potentially migrating from hashlru to toad-cache -- encapsulate the lru as a decorator.

This will:

• make the tests agnostic to underlying cache implementations
• aid in benchmarking differences between cache implementations
• drop a devDependency

Benchmarks

Benchmark		Node 18 PR	Node 18 Base		Node 20 PR	Node 20 Base		Node 21 PR	Node 21 Base
express.js		8351	8231		8815	8591		8439	8447
fastify.js		42975	41247		43391	42687		42271	42463
fastify-art.js		9511	9431		10487	11567		9287	9271
fastify-dot.js		47199	46367		47615	46751		47839	46975
fastify-eta.js		27199	27007		30095	29327		37695	35327
fastify-pug.js		45183	45759		46367	44735		46719	46559
fastify-twig.js		30175	35423		38911	38335		40831	39167
fastify-liquid.js		7531	6323		7663	7667		7803	7711
fastify-mustache.js		31855	31503		34079	35423		33887	33951
fastify-nunjucks.js		41599	41631		42655	43167		43295	42463
fastify-ejs-async.js		35039	35647		43263	44095		45247	43327
fastify-ejs-minify.js		11855	12567		14463	15383		13823	14407
fastify-handlebars.js		25231	25647		31055	31727		26495	27679
fastify-ejs-local-layout.js		26831	26159		31487	31583		31039	31167
fastify-ejs-global-layout.js		34527	32479		34975	40543		40159	41375

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[mcollina]

lgtm

[mweberxyz]

Merge conflicts resolved.