Add comprehensive test suite and documentation

- Complete unit, integration, and E2E test coverage (189 test cases)
- Enhanced CI/CD pipeline with race detection and quality checks
- Comprehensive godoc documentation for all packages
- Updated README with API docs, examples, and deployment guides

.drone.yml

@@ -9,9 +9,17 @@ steps:
   volumes:
   - name: deps
     path: /go
+  environment:
+    CGO_ENABLED: 1
   commands:
-  - go test -v
+  - go mod download
+  - go test -v ./...
+  - go test -race ./...
+  - go test -short ./...
   - go build
+  - go vet ./...
+  - go tool gofumpt -l .
+  - go mod verify
 
 - name: docker
   image: harbor.ntppool.org/ntppool/drone-kaniko:main
@@ -23,14 +31,19 @@ steps:
     repo: ntppool/geoipapi
     registry: harbor.ntppool.org
     auto_tag: true
-    tags: SHA7,${DRONE_SOURCE_BRANCH}
+    tags: "${DRONE_BRANCH},build-${DRONE_BUILD_NUMBER},SHAABBREV,SHA7"
     cache: true
     username:
       from_secret: harbor_username
     password:
       from_secret: harbor_password
+
+volumes:
+- name: deps
+  temp: {}
+
 ---
 kind: signature
-hmac: 0c52196c25e55d77d014865c7a0298b24849133f9f59b14ca9fd235917f2649d
+hmac: a7bb16cf7f4a0195435980fb6a90b9d1092a50c1dba87636dae891600f4b86b0
 
 ...