fix: split Dockerfile with pinned images and add CI workflow

- Pin golangci-lint to v1.64.8 by sha256 digest
- Pin golang to 1.22.12 by sha256 digest
- Lint stage runs make fmt-check + make lint
- Test stage runs make test with dependency on lint stage
- Remove redundant final stage (library has no binary)
- Add fmt-check, check, hooks targets to Makefile
- Add .gitea/workflows/check.yml for CI

closes #9

Dockerfile

@@ -1,39 +1,20 @@
-# First stage: Use the golangci-lint image to run the linter
-FROM golangci/golangci-lint:latest as lint
-
-# Set the Current Working Directory inside the container
-WORKDIR /app
-
-# Copy the go.mod file and the rest of the application code
-COPY go.mod ./
+# Lint stage: format check + golangci-lint
+# golangci-lint v1.64.8 (2025-02-18)
+FROM golangci/golangci-lint@sha256:2987913e27f4eca9c8a39129d2c7bc1e74fbcf77f181e01cea607be437aa5cb8 AS lint
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
 COPY . .
+RUN make fmt-check
+RUN make lint
 
-# Run golangci-lint
-RUN golangci-lint run
-
-RUN sh -c 'test -z "$(gofmt -l .)"'
-
-# Second stage: Use the official Golang image to run tests
-FROM golang:1.22 as test
-
-# Set the Current Working Directory inside the container
-WORKDIR /app
-
-# Copy the go.mod file and the rest of the application code
-COPY go.mod ./
+# Test stage: run full test suite
+# golang 1.22.12 (2025-02-04)
+FROM golang@sha256:1cf6c45ba39db9fd6db16922041d074a63c935556a05c5ccb62d181034df7f02 AS test
+# Depend on lint stage so both stages always run
+COPY --from=lint /src/go.sum /dev/null
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
 COPY . .
-
-# Run tests
-RUN go test -v ./...
-
-# Final stage: Combine the linting and testing stages
-FROM golang:1.22 as final
-
-# Ensure that the linting stage succeeded
-WORKDIR /app
-COPY --from=lint /app .
-COPY --from=test /app .
-
-# Set the final CMD to something minimal since we only needed to verify lint and tests during build
-CMD ["echo", "Build and tests passed successfully!"]
-
+RUN make test