Improve performance of find_by_iso_numeric method

[pranavbabu]

ruby 3.3.3 (2024-06-12 revision f1c7b6f435) [arm64-darwin23]
Warming up --------------------------------------
 Before optimization     2.135k i/100ms
  After optimization    55.681k i/100ms
Calculating -------------------------------------
 Before optimization     21.148k (± 0.8%) i/s   (47.29 μs/i) -    106.750k in   5.048173s
  After optimization    549.315k (± 0.6%) i/s    (1.82 μs/i) -      2.784M in   5.068425s

Comparison:
  After optimization:   549314.7 i/s
 Before optimization:    21147.5 i/s - 25.98x  slower

[sunny]

Nice performance gains! 😍

[sunny]

Shouldn’t this memoisation be cleared/updated when registering new currencies?

For example if I called this in my code, wouldn’t I get unexpected results?

unless Money::Currency.find_by_iso_numeric(250)
  # ^---- this would fill `@iso_numeric_index` from `@table`

  Money::Currency.register({
    priority:            1,
    iso_code:            "FRF",
    iso_numeric:         "250",
    name:                "French Francs",
    symbol:              "FR",
    subunit:             "Centimes",
    subunit_to_unit:     100,
    decimal_mark:        ",",
    thousands_separator: " "
  })
  # ^--- this would add a new entry to `@table`
end

Money::Currency.find_by_iso_numeric(250) # => nil ⚠️
# ^--- this would use the `@iso_numeric_index` and not `@table`

Also, it should probably be cleared inside the reset! method as well.