Update AddressMapper.kt

[GeorgCantor]

Use of flatMap:
The flatMap function is used to transform each AddressComponent into pairs of type and the component itself. This flattens the structure into a single list of pairs, making it easier to group by type.

Use of groupBy:
The groupBy function is then applied to this list of pairs. It takes a selector for the key (the type) and a selector for the value (the AddressComponent). This eliminates the need for manual initialization and population of the map.

Immutable Map:
The result is an immutable Map<String, List>, which is generally preferred in Kotlin for better safety and clarity.

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[dkhawk]

Thanks for opening this PR! Before we merge it, could you please take a look at the commit messages? We're using Conventional Commits to help keep our commit history organized, and it looks like this doesn't follow that format. Also, please update the PR title to have a conventional commit prefix.

Thanks again and let me know if you have any questions!