feat(zns-importer): add ZNSImportService with tests and REST controller

- Created `ZnsImportService` to handle uploading, parsing, and persisting ZNS data from legacy `.zip` files.
- Introduced corresponding test cases in `ZnsImportServiceTest` for handling edge cases including imports and updates.
- Added REST controller `ZnsImportController` for initiating import jobs and retrieving their status.
- Defined `ZnsImportResult` data structure for reporting results of import operations.
- Established database configuration specific to ZNS importer for development profile.
- Updated utility libraries with `FixedWidthLineReader` for fixed-width string parsing.
- Refactored architecture by placing parser logic in `core:zns-parser` for reuse across backend and Compose Desktop app.

Signed-off-by: Stefan Mogeritsch <stefan.mo.co@gmail.com>

backend/services/zns-import/zns-import-service/src/main/resources/application.yaml

@@ -0,0 +1,34 @@
+server:
+  port: ${ZNS_IMPORT_SERVER_PORT:8095}
+
+spring:
+  application:
+    name: zns-import-service
+  profiles:
+    active: ${SPRING_PROFILES_ACTIVE:dev}
+  datasource:
+    url: ${SPRING_DATASOURCE_URL:jdbc:postgresql://localhost:5432/pg-meldestelle-db}
+    username: ${SPRING_DATASOURCE_USERNAME:pg-user}
+    password: ${SPRING_DATASOURCE_PASSWORD:pg-password}
+    driver-class-name: org.postgresql.Driver
+  servlet:
+    multipart:
+      enabled: true
+      max-file-size: 50MB
+      max-request-size: 50MB
+  autoconfigure:
+    exclude:
+      - org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration
+      - org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration
+
+management:
+  endpoints:
+    web:
+      exposure:
+        include: health,info,metrics
+  endpoint:
+    health:
+      show-details: always
+
+app:
+  service-name: ${spring.application.name}