fix: add OS version to cache key to prevent binary incompatibility (#716)

## Summary

- Adds OS name and version (e.g., `ubuntu-22.04`, `macos-14`,
`windows-2022`) to cache keys to prevent binary incompatibility when
GitHub updates runner images
- Fixes issue where cached uv binaries compiled against older
glibc/library versions fail on newer runner OS versions

## Changes

- Added `getOSNameVersion()` function to `src/utils/platforms.ts` with
OS-specific detection for Linux (via `/etc/os-release`), macOS (Darwin
kernel version mapping), and Windows
- Updated cache key format to include OS version, bumped `CACHE_VERSION`
to `"2"`
- Added `cache-key` output to expose the generated cache key for
debugging
- Added `test-cache-key-os-version` job testing across multiple OS
versions
- Updated `docs/caching.md` with cache key documentation

Closes #703

src/cache/restore-cache.ts

@@ -13,15 +13,16 @@ import {
   restoreCache as shouldRestoreCache,
   workingDirectory,
 } from "../utils/inputs";
-import { getArch, getPlatform } from "../utils/platforms";
+import { getArch, getOSNameVersion, getPlatform } from "../utils/platforms";
 
 export const STATE_CACHE_KEY = "cache-key";
 export const STATE_CACHE_MATCHED_KEY = "cache-matched-key";
-const CACHE_VERSION = "1";
+const CACHE_VERSION = "2";
 
 export async function restoreCache(): Promise<void> {
   const cacheKey = await computeKeys();
   core.saveState(STATE_CACHE_KEY, cacheKey);
+  core.setOutput("cache-key", cacheKey);
 
   if (!shouldRestoreCache) {
     core.info("restore-cache is false. Skipping restore cache step.");
@@ -72,9 +73,10 @@ async function computeKeys(): Promise<string> {
   const suffix = cacheSuffix ? `-${cacheSuffix}` : "";
   const pythonVersion = await getPythonVersion();
   const platform = await getPlatform();
+  const osNameVersion = getOSNameVersion();
   const pruned = pruneCache ? "-pruned" : "";
   const python = cachePython ? "-py" : "";
-  return `setup-uv-${CACHE_VERSION}-${getArch()}-${platform}-${pythonVersion}${pruned}${python}${cacheDependencyPathHash}${suffix}`;
+  return `setup-uv-${CACHE_VERSION}-${getArch()}-${platform}-${osNameVersion}-${pythonVersion}${pruned}${python}${cacheDependencyPathHash}${suffix}`;
 }
 
 async function getPythonVersion(): Promise<string> {