Improve offline search cache

[Jikoo]

Offline search currently has a very small cache of only the most recent results.
This is particularly problematic for servers with large playerbases - cache misses will be frequent, resulting in thousands of wasteful system calls. We should instead move to a single larger cache on disk.

Pros:

• Easily locate results of prior queries
• Indexable for faster searching/matching

Cons:

• Uses more disk space
  • Generally would be storing 2-4 strings per player - not a huge concern
• Requires keeping a file open
  • Mitigated by the fact that offline matching would no longer open every single player file (admittedly, sequentially)

Another potential plan is to move offline name matching to a separate searching command, but more casual users (aka the majority of the users) will likely find this a nuisance.