feat(wasm): add support for OCI urls

[bobdoah]

This change adds OCI support for WASM plugin URLs. The OCI artifact is checked against the CNCF Wasm OCI artifact layout.

An example of building and using the sqlc-gen-go plugin via OCI:

1. Build the plugin

git clone https://github.com/sqlc-dev/sqlc-gen-go.git
cd sqlc-gen-go
make bin/sqlc-gen-go.wasm
cd bin

2. Create the OCI config

WASM_SHA256=$(sha256sum sqlc-gen-go.wasm | awk '{print $1}')

cat > config.json <<EOF
{
  "architecture": "wasm",
  "os": "wasip1",
  "layerDigests": ["sha256:${WASM_SHA256}"]
}
EOF

3. Authenticate and push

IMAGE=ghcr.io/bobdoah/sqlc-gen-go

oras login ghcr.io

oras push "${IMAGE}:v1" \
  --config config.json:application/vnd.wasm.config.v0+json \
  sqlc-gen-go.wasm:application/wasm

The config is uploaded as the manifest’s config blob; the WASM file is its only layer.

4. Configure sqlc

cat > examples/authors/oci-sqlc.yaml << EOF
version: "2"
plugins:
  - name: golang
    wasm:
      url: oci://${IMAGE}:v1@$(oras resolve "${IMAGE}:v1")
      sha256: $WASM_SHA256

sql:
- engine: sqlite
  schema: sqlite/schema.sql
  queries: sqlite/query.sql
  codegen:
  - plugin: golang
    out: gen
    options:
      package: authors
EOF

5. Run the example

make sqlc-dev
~/bin/sqlc-dev generate -f examples/authors/oci-sqlc.yaml