refactor: simplify commentsCount logic

[iuioiua]

This will either fix the current server-side error or help in diagnosing it.

An error occurred during route handling or page rendering. TypeError: Error parsing args at position 2: expected string, number, bigint, ArrayBufferView, boolean
    at Object.opAsync (ext:core/01_core.js:256:30)
    at KvListIterator.<anonymous> (ext:deno_kv/01_db.ts:107:42)
    at KvListIterator.next (ext:deno_kv/01_db.ts:379:48)
    at getItemCommentsCountsByIds (file:///src/utils/db.ts:105:26)
    at eventLoopTick (ext:core/01_core.js:165:11)
    at async GET (file:///src/routes/index.tsx:11:32)
    at async https://deno.land/x/rutt@0.1.0/mod.ts:143:36
    at async handler (file:///src/routes/_middleware.ts:26:22)
    at async Server.handler (https://deno.land/x/fresh@1.1.5/src/server/context.ts:220:25)
    at async Server.#respond (https://deno.land/std@0.178.0/http/server.ts:220:24)