Introducing district and subdistrict field labels and error strings

[ananyaneogi]

What are you trying to accomplish?

Add support for district and subdistrict as address fields, enabling regions to collect and validate these address components. This is needed to support address formats in countries where district and subdistrict are meaningful parts of a postal address (e.g., Brazil, Philippines, Kuwait, Peru).

Also cut a new minor version.

What approach did you choose and why?

district and subdistrict were added following the same pattern already established by neighborhood, street_name, etc -

• Both fields are added as attributes on the Address class with reader accessors and constructor parameters.
• Both are registered in Field as recognized field keys.
• Translations for validation error/warning messages are added

What should reviewers focus on?

Are the changes sufficient to introduce new error translations and labels to clients?

The impact of these changes

Consumers of this gem can now use district and subdistrict address fields with full label and validation message support. Existing addresses without these fields are unaffected, as both default to nil.

Testing

New tests cover:

• Initializing an Address with district and subdistrict and reading their values back.
• Verifying that format correctly fills {district} and {subdistrict} placeholders in additional lines.
• Confirming that nil is the default for both fields when omitted.
• Asserting correct error messages for district and subdistrict across BR, KW, PE, and PH.
• Asserting correct labels for district and subdistrict across multiple locales and countries.

Checklist

• I have added a CHANGELOG entry for this change (or determined that it isn't needed)