Speed up `ja/address.yml` loading

[thdaraujo]

(related to #2719)

Japanese postal codes were changed from a pattern to a list of real postal codes, introduced in #2297.

The problem is that when running Faker on locale = 'ja', about 60% of the time to load and call Address#postalcode is spent reading and parsing the ja/address.yml file, which has 2.2mb.

Benchmark:

Postcode - Smaller Address File:  1.2 i/s
Postcode:                         0.7 i/s - 1.65x  slower

1.34 s/i vs 811.55 ms/i

Let's come up with a way to improve this.