refactor: simplify split-cache handling

Restore cache entries sequentially, keep saves parallel with per-entry error handling, and simplify the cache test setup.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

__tests__/cache-utils.test.ts

@@ -1,14 +1,4 @@
-import {
-  jest,
-  describe,
-  it,
-  expect,
-  beforeEach,
-  afterEach,
-  afterAll
-} from '@jest/globals';
-import fs from 'fs';
-import path from 'path';
+import {jest, describe, it, expect, beforeEach, afterAll} from '@jest/globals';
 
 jest.unstable_mockModule('@actions/exec', () => ({
   exec: jest.fn(),
@@ -212,139 +202,6 @@ describe('getCacheDirectoryPath', () => {
   });
 });
 
-describe('canRestoreCachesInParallel', () => {
-  const originalPlatform = Object.getOwnPropertyDescriptor(
-    process,
-    'platform'
-  )!;
-  const directoryStat = fs.lstatSync(process.cwd());
-
-  beforeEach(() => {
-    Object.defineProperty(process, 'platform', {value: 'linux'});
-    jest.spyOn(fs, 'lstatSync').mockReturnValue(directoryStat);
-    jest
-      .spyOn(fs, 'realpathSync')
-      .mockImplementation(directory => path.resolve(directory.toString()));
-  });
-
-  afterEach(() => {
-    Object.defineProperty(process, 'platform', originalPlatform);
-    jest.restoreAllMocks();
-  });
-
-  it.each([
-    {modules: 'cache/modules', build: 'cache/build', parallel: true},
-    {modules: 'cache', build: 'cache-build', parallel: true},
-    {modules: 'cache', build: 'cache', parallel: false},
-    {modules: 'cache', build: 'cache/build', parallel: false},
-    {modules: 'cache/modules', build: 'cache', parallel: false},
-    {modules: 'cache', build: 'cache/../cache', parallel: false}
-  ])(
-    'checks overlapping paths: $modules and $build',
-    ({modules, build, parallel}) => {
-      expect(
-        cacheUtils.canRestoreCachesInParallel([
-          {kind: 'modules', path: modules},
-          {kind: 'build', path: build}
-        ])
-      ).toBe(parallel);
-    }
-  );
-
-  it('allows concurrent Windows restores with disjoint paths', () => {
-    Object.defineProperty(process, 'platform', {value: 'win32'});
-
-    expect(
-      cacheUtils.canRestoreCachesInParallel([
-        {kind: 'modules', path: 'cache/modules'},
-        {kind: 'build', path: 'cache/build'}
-      ])
-    ).toBe(true);
-  });
-
-  it.each(['darwin', 'win32'])(
-    'handles case-insensitive paths conservatively on %s',
-    platform => {
-      Object.defineProperty(process, 'platform', {value: platform});
-
-      expect(
-        cacheUtils.canRestoreCachesInParallel([
-          {kind: 'modules', path: 'cache'},
-          {kind: 'build', path: 'CACHE/build'}
-        ])
-      ).toBe(false);
-    }
-  );
-
-  it.each([true, false])(
-    'serializes symlink aliases with missing cache directories (overlap=%s)',
-    overlap => {
-      const alias = path.resolve('alias');
-      const target = path.resolve('target');
-      jest.spyOn(fs, 'lstatSync').mockImplementation(directory => {
-        if (directory !== alias && directory !== target) {
-          throw Object.assign(new Error('Missing path'), {code: 'ENOENT'});
-        }
-        return directoryStat;
-      });
-      jest.spyOn(fs, 'realpathSync').mockReturnValue(target);
-
-      expect(
-        cacheUtils.canRestoreCachesInParallel([
-          {kind: 'modules', path: path.join(alias, 'modules')},
-          {
-            kind: 'build',
-            path: path.join(target, overlap ? 'modules/build' : 'build')
-          }
-        ])
-      ).toBe(false);
-    }
-  );
-
-  it.each(['nested alias', 'alias through module cache'])(
-    'serializes restores when the %s resolves outside the module cache',
-    scenario => {
-      const modules = path.resolve('modules');
-      const target = path.resolve('external-build');
-      const alias = path.join(modules, 'build-link');
-      const build =
-        scenario === 'nested alias'
-          ? path.join(alias, 'cache')
-          : path.resolve('build-alias', 'cache');
-      jest.spyOn(fs, 'realpathSync').mockImplementation(directory => {
-        const absolute = path.resolve(directory.toString());
-        if (absolute === build) {
-          return path.join(target, 'cache');
-        }
-        if (absolute === path.dirname(build)) {
-          return scenario === 'nested alias' ? target : alias;
-        }
-        return absolute;
-      });
-
-      expect(
-        cacheUtils.canRestoreCachesInParallel([
-          {kind: 'modules', path: modules},
-          {kind: 'build', path: build}
-        ])
-      ).toBe(false);
-    }
-  );
-
-  it('falls back to sequential restores when path resolution fails', () => {
-    jest.spyOn(fs, 'realpathSync').mockImplementation(() => {
-      throw new Error('Cannot resolve path');
-    });
-
-    expect(
-      cacheUtils.canRestoreCachesInParallel([
-        {kind: 'modules', path: 'cache/modules'},
-        {kind: 'build', path: 'cache/build'}
-      ])
-    ).toBe(false);
-  });
-});
-
 describe('isCacheFeatureAvailable', () => {
   //Arrange
   const isFeatureAvailableSpy = cache.isFeatureAvailable as jest.Mock<