Resolve an environment value the same way regardless of host, so middleware never branch on Deno vs process vs a Workers bindings object.
Resolution order:
process.env where a process global exists (Node, Bun, Deno 2, Workers with nodejs_compat), via std-env,Deno.env.get on Deno hosts without a populated process.env.On Workers, bindings are per-request, so this returns undefined at module top level until the first request has been handled.