fix(server/accounts): return cached account instance in OxAccount.get

[DoluTattoo]

Problem

OxAccount.get never returns its cached instance:

static async get(accountId: number) {
  if (accountId in this.members) this.members[accountId];

  const validAccount = await SelectAccount(accountId);
  ...
  return new OxAccount(accountId);
}

this.members[accountId] is an expression statement, so the looked-up value is discarded. Every call falls through to SelectAccount and constructs a new OxAccount, which makes the cache write-only — the eviction interval in server/accounts/index.ts has nothing to evict that was ever read.

Because ClassInterface.add returns early when the id is already registered, the registry keeps the very first instance while every later caller receives a throwaway one. The extra instances are not leaked, but each lookup pays for a redundant SELECT.

Fix

Return the cached instance when one exists.

Behaviour

Identical, minus the redundant query:

• DeleteAccount only sets type = 'inactive' and never deletes the row, and SelectAccount does not filter on type. So a cached accountId always still resolves in the database — the SELECT could never turn a cache hit into the No account exists error.
• OxAccount holds no mutable state beyond accountId, so a cached instance is equivalent to a freshly constructed one.

Impact

Minor. The wasted query is a primary-key lookup, so this is a correctness/hygiene fix rather than a performance emergency. Note that GetCharacterAccount and GetGroupAccount still run SelectDefaultAccountId beforehand, so only the second query is avoided on those paths.