[antithesis] Enable image build for multi-module repos

The proposed subnet-evm refactor requires that construction of the
builder image support providing the path to the go module whose
dependencies will be downloaded.

scripts/lib_build_antithesis_images.sh

@@ -16,6 +16,7 @@ function build_antithesis_builder_image {
   local image_name=$2
   local avalanchego_path=$3
   local target_path=$4
+  local module_path=${5:-}
 
   local base_dockerfile="${avalanchego_path}/tests/antithesis/Dockerfile"
   local builder_dockerfile="${base_dockerfile}.builder-instrumented"
@@ -25,7 +26,8 @@ function build_antithesis_builder_image {
     builder_dockerfile="${base_dockerfile}.builder-uninstrumented"
   fi
 
-  docker buildx build --build-arg GO_VERSION="${go_version}" -t "${image_name}" -f "${builder_dockerfile}" "${target_path}"
+  docker buildx build --build-arg GO_VERSION="${go_version}" --build-arg=MODULE_PATH="${module_path}" \
+         -t "${image_name}" -f "${builder_dockerfile}" "${target_path}"
 }
 
 # Build the antithesis node, workload, and config images.

tests/antithesis/Dockerfile.builder-uninstrumented

@@ -5,13 +5,20 @@ ARG GO_VERSION
 FROM golang:$GO_VERSION-bullseye
 
 WORKDIR /build
-# Copy and download dependencies using go mod
-COPY go.mod .
-COPY go.sum .
-RUN go mod download
 
 # Copy the code into the container
 COPY . .
 
+# Download dependencies of the main go module
+RUN go mod download
+
+# Providing a non-empty MODULE_PATH supports the case where the target module is
+# not at the root of the repo but its go.mod references other modules in the repo
+# (including the root).
+ARG MODULE_PATH
+
+# Download dependencies for the specified go module if a path was provided
+RUN [ -n $MODULE_PATH ] && (cd $MODULE_PATH && go mod download) || true
+
 # Ensure pre-existing builds are not available for inclusion in the final image
 RUN [ -d ./build ] && rm -rf ./build/* || true