Add generic postcode/address lookup with pluggable drivers

[claudio-ferraro]

Summary

• rapidez/postcode is a generic postcode/address lookup package with a pluggable driver architecture, instead of building yet another single-purpose package
• Ships with three drivers: postcodeeu (Postcode.eu), pro6pp (Pro6pp), postcodeservice (Postcodeservice); each calling its API directly from Rapidez, no Magento dependency required for the lookup
• Uses the same postcode-change Vue event already wired into Rapidez's own address form, so it works out of the box with no Blade template changes
• Adding a future driver only requires a new class + a config entry; no changes to the route, controller or JavaScript
• Requires rapidez/core ^5.0 (relies on the event helper introduced in v5)

Test plan

• PHPStan (level 1) passes
• All three drivers verified directly (valid lookup, invalid/not-found lookup, validation, caching)
• All three drivers verified end-to-end in a Rapidez v5 project: checkout address, and account address book
• House number addition handling verified for both the dedicated addition field and the combined house-number-field case
• Driver switching verified to be a pure .env/config change, no code changes needed

ref: RAP-2028

[Jade-GG]

I notice that this only supports dutch postcodes right now, is that correct? If this is intended, the readme should probably reflect that.

[Jade-GG]

As far as I know, in other packages we put this under just ...\Data, but I'm not 100% confident on that so double check this before changing anything

[claudio-ferraro]

Double-checked this, couldn't find that convention anywhere (searched in our Rapidez packages' file trees plus a full code search). Keeping DataTransferObjects for now, happy to revisit if you know of one I missed.