Reverts HUF subunits back to ISO 4217

[matid]

Subunits of Hungarian forint are no longer in circulation and were eliminated in #679.
However, ISO continues to treat HUF as a two decimal place currency.
This can be confirmed against the standard here: https://www.six-group.com/dam/download/financial-information/data-center/iso-currrency/lists/list-one.xml

To align Money with the ISO 4217 standard, this change restores original behavior of considering HUF a 2 decimal point currency.

[sunny]

I’m wary of introducing this change, since codebases using this have been relying on having no subunit.

Could we add a changelog entry describing the breaking change with some code to add to an app that would keep the previous behavior? 🙏🏻

[tagliala]

For new maintainers: please note that this PR and #1092 take opposite approaches regarding subunit definitions

This PR aligns HUF with ISO 4217, using 2 decimals even though subunits are obsolete. In contrast, #1092 sets ALL to 0 decimals to match JavaScript’s Intl.NumberFormat, even though ISO 4217 specifies 2 decimals for ALL.

I recommend that the library choose a clear, consistent standard. If developers need to match application-specific behavior (like JavaScript’s formatting), they can override the defaults as needed. Consistency will help reduce confusion and make maintenance easier for everyone.

I would personally merge this PR, document the breaking change, and mark as "won't fix" the other one

I've created a table to compare ISO 4217 and JS's https://gist.github.com/tagliala/9769f26ab300d5a156e1e4893c5e4d51 (note: the script is AI generated)

It appears that Chrome's JS engine is not respecting the ISO standard, Firefox does

[matid]

Shopify/money aligns standard subunits to ISO 4217 but has support for converters that align subunits to other formats (like Stripe’s) if someone's looking for an alternative solution to this.

[sunny]

@matid Shouldn’t we also need to change the smallest_denomination and subunit entries here?

As for the changelog, I was thinking of something like this to ease the upgrade:

- **Breaking change**: Fix HUF back to 2 decimals to align with ISO 4217
  (change subunit_to_unit from 1 to 100).

  To keep the previous behavior, call:

  ```rb
  Money::Currency.register(
    **Money::Currency.table[:huf],
    subunit_to_unit: 1,
    subunit: "",
    smallest_denomination: 5,
  )