CI, sonic: Replace backend-arm64 docker build with native GHA runner, disable sonic for arm64 (#1794)

* CI: Replace docker amd64 with native runner, switch Docker test arch to amd64

* tests: Remove spaces and new lines from test JSON timestamp fields

* builds: Disable sonic for arm64 due to OKX unmarshal issue

* nits: Improve Dockerfile comment and fix build tag

.github/workflows/amd64.Dockerfile

@@ -0,0 +1,13 @@
+FROM golang:1.23-alpine
+
+# Install GCC and musl-dev (needed for SQLite library)
+RUN apk add --no-cache gcc musl-dev
+
+WORKDIR /app
+
+COPY go.mod go.sum ./
+RUN go mod download && go mod verify
+
+COPY . /app
+
+CMD ["go", "test", "./..."]