fix(core): prevent concurrent downloads clobbering by using unique temp dirs

[emyjamalian]

• This change ensures concurrent 'npx playwright install' processes do not clobber each other by downloading to a unique temporary directory before finalizing.
• Adds unique temp dir per download in packages/playwright-core/src/server/registry/browserFetcher.ts.
• Adds installation test tests/installation/concurrent-download.spec.ts validating concurrent installs.
• Test assertions avoid depending on stdout formatting.
• Fixes [Bug]: Jobs running concurrently on the same machine download browsers to the same directory and clobber each other (Windows) #32179

[emyjamalian]

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[github-actions]

Test results for "tests 1"

2 failed
❌ [firefox-page] › page/page-route.spec.ts:515 › should work with encoded server - 2 @firefox-ubuntu-22.04-node18
❌ [installation tests] › concurrent-download.spec.ts:20 › concurrent browser downloads should not clobber each other @package-installations-windows-latest

3 flaky

⚠️ [firefox-library] › library/inspector/cli-codegen-1.spec.ts:1079 › cli codegen › should not throw csp directive violation errors `@firefox-ubuntu-22.04-node18`
⚠️ [playwright-test] › ui-mode-trace.spec.ts:397 › should work behind reverse proxy `@macos-latest-node18-1`
⚠️ [playwright-test] › ui-mode-test-output.spec.ts:80 › should show console messages for test `@ubuntu-latest-node18-1`

46842 passed, 821 skipped

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Merge workflow run.

[yury-s]

The new test is failing on Windows.

[yury-s]

All 3 commands will try to install browsers into the same directory, which may lead to the test flakiness. Please make sure the the commands run with different PLAYWRIGHT_BROWSERS_PATH values, something like:

    await Promise.all(Array.from({ length: numProcesses }, (_, index) =>
      exec('npx playwright install chromium', {
        env: {
          PLAYWRIGHT_BROWSERS_PATH: test.info().outputPath(`browsers-${index}`),
        }
      })
    ));