`purlbatch` fails for valid Go PURLs but `versionbatch` works

Hi deps.dev team 👋

I’ve run into an inconsistency between the `purlbatch` endpoint and the `versionbatch` endpoint.

---

### Problem

When querying a valid Go module version via `purlbatch`, I get nothing.

**Failing request (purlbatch):**

```bash
curl -X POST 'https://api.deps.dev/v3alpha/purlbatch' \
-H 'Content-Type: application/json' \
-d '{
"requests": [
{"purl": "pkg:golang/github.com/cyclonedx/cyclonedx-go@v0.9.2"}
]
}'
```

**Response:**

```json
{
"responses": [
{
"request": {
"purl": "pkg:golang/github.com/cyclonedx/cyclonedx-go@v0.9.2"
}
}
],
"nextPageToken": ""
}
```

---

### Expected behavior

The above `purlbatch` call should return metadata for `cyclonedx-go v0.9.2`, which exists in deps.dev.

---

### Actual behavior

`purlbatch` returns nothing, but the same package works with `versionbatch`.

**Working request (versionbatch):**

```bash
curl -X POST 'https://api.deps.dev/v3alpha/versionbatch' \
-H 'Content-Type: application/json' \
-d '{
"requests":[
{
"versionKey":{
"system":"GO",
"name":"github.com/CycloneDX/cyclonedx-go",
"version":"v0.9.2"
}
}
]
}'
```

**Response:**

```json
{
"responses": [
{
"request": {
"versionKey": {
"system": "GO",
"name": "github.com/CycloneDX/cyclonedx-go",
"version": "v0.9.2"
}
},
"version": {
"versionKey": {
"system": "GO",
"name": "github.com/CycloneDX/cyclonedx-go",
"version": "v0.9.2"
},
"purl": "pkg:golang/github.com/cyclonedx/cyclonedx-go@v0.9.2",
"publishedAt": "2024-12-13T14:41:43Z",
"isDefault": true,
"isDeprecated": false,
"licenses": [
"Apache-2.0"
],
"licenseDetails": [
{
"license": "Apache-2.0",
"spdx": "Apache-2.0"
}
],
"advisoryKeys": [],
"links": [
{
"label": "SOURCE_REPO",
"url": "https://github.com/CycloneDX/cyclonedx-go"
}
],
"slsaProvenances": [],
"attestations": [],
"registries": [],
"relatedProjects": [
{
"projectKey": {
"id": "github.com/cyclonedx/cyclonedx-go"
},
"relationProvenance": "GO_ORIGIN",
"relationType": "SOURCE_REPO"
}
],
"upstreamIdentifiers": [
{
"packageName": "github.com/CycloneDX/cyclonedx-go",
"versionString": "v0.9.2",
"source": "GO_MODULE_PROXY"
}
]
}
}
],
"nextPageToken": ""
}
```

---

### Observations

* The package **does exist** in BigQuery with PURL:

```
pkg:golang/github.com/cyclonedx/cyclonedx-go@v0.9.2
```
* `versionbatch` resolves correctly with canonical module name (`github.com/CycloneDX/cyclonedx-go`).
* `purlbatch` seems to mishandle Go PURLs which is the same purl returned in the version batch api.

---

### Impact

* It’s currently impossible to reliably fetch certain Go packages via PURL (`purlbatch`)

---

### Workaround

* Use `versionbatch` with `system=GO` and the canonical module path.