fix: Hugo package naming fix (#688)

## Summary

Rebases the Hugo package naming fix from #609 on top of the current
`main` branch, including the installer flow added in #687.

- Derive Hugo release asset OS and architecture naming conventions from
the requested Hugo version.
- Apply those conventions when selecting OS and architecture segments,
including the 0.102.x macOS universal boundary, 0.103+ downcased OS
names, Windows zip assets, and Linux ARM assets.
- Add table-driven tests for pre-0.102, 0.102.x, and 0.103+ naming
behavior, plus URL coverage for the corrected release asset names.

## Changes

- Add `getConventions` to centralize version-based release asset naming
decisions.
- Update `getOS` and `getArch` to use convention flags for macOS,
lower-case OS names, standardized architecture names, and the Windows
ARM support boundary.
- Update `getURL` to generate candidate URLs for downcased Windows and
Linux assets, and for darwin universal archives.
- Wire convention detection into `installer` before generating candidate
Hugo release asset URLs.
- Expand unit coverage for OS, architecture, convention, and URL
behavior.

## Checklist

- [x] I have read the latest README and followed the instructions.
- [x] I have added or updated tests for behavior changes.
- [x] README.md and action.yml updates are not needed because inputs and
action metadata are unchanged.
- [x] I have run the relevant verification commands.

## References

- Rebased follow-up for
https://github.com/peaceiris/actions-hugo/pull/609
- References https://github.com/peaceiris/actions-hugo/issues/605 and
https://github.com/peaceiris/actions-hugo/issues/608
- Based on `main` after
https://github.com/peaceiris/actions-hugo/pull/687

## Verification

- [x] `RUNNER_TEMP=/private/tmp npm run all`
- [ ] `npm run build` was not run because this branch does not update
bundled output and current `main` removed `lib/index.js`.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Version-aware conventions control OS and architecture naming,
including macOS universal asset support and expanded darwin/macOS
patterns.

* **Refactor**
* Conventions centralized and applied across installer and URL
generation; OS/arch inputs accept varied casing and naming variants.

* **Tests**
* Expanded, data-driven parameterized tests for conventions, OS/arch
mappings, URL variants, and error cases.
* Replaced network stubs with deterministic fetch-mock helpers for test
isolation.

[![Review Change
Stack](https://storage.googleapis.com/coderabbit_public_assets/review-stack-in-coderabbit-ui.svg)](https://app.coderabbit.ai/change-stack/peaceiris/actions-hugo/pull/688)
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Michael T Lombardi <michael.t.lombardi@gmail.com>
Co-authored-by: codefactor-io <support@codefactor.io>
Co-authored-by: Codex <noreply@openai.com>

__tests__/mocks/node-fetch.ts

@@ -22,8 +22,35 @@ interface ResponseLike {
   json: () => Promise<unknown>;
 }
 
+interface MockResponse {
+  body?: unknown;
+  status: number;
+}
+
+const mockResponses = new Map<string, MockResponse>();
+
+export function mockFetchResponse(url: string, status: number, body?: unknown): void {
+  mockResponses.set(url, {
+    body,
+    status
+  });
+}
+
+export function clearMockFetchResponses(): void {
+  mockResponses.clear();
+}
+
 export default async function fetch(url: string | URL): Promise<ResponseLike> {
   const target = url.toString();
+  const mockResponse = mockResponses.get(target);
+  if (mockResponse) {
+    return {
+      ok: mockResponse.status >= 200 && mockResponse.status < 300,
+      status: mockResponse.status,
+      json: async () => mockResponse.body as unknown
+    };
+  }
+
   const client = target.startsWith('https:') ? https : http;
 
   return new Promise((resolve, reject) => {