test: configure network-timeout and prefer-offline for yarn in e2e tests

[alan-agius4]

PR Checklist

Please check to confirm your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Yarn Classic in the E2E test sandbox defaults to a 30-second socket timeout and performs multiple sequential retries on network stalls, which can cause shards with multiple package installations to run for excessive amounts of time when external registry latency or socket stalls occur.

What is the new behavior?

Configures .yarnrc with network-timeout 15000 and prefer-offline true in the E2E npm sandbox (tests/e2e/setup/001-npm-sandbox.ts) to fail faster on stalled connections and avoid hanging during package resolution while remaining resilient to transient CI latency.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[gemini-code-assist]

Code Review

This pull request defines a new WEBPACK_TESTS list in tests/e2e.bzl and configures webpack e2e suites to use it. It also updates the Yarn sandbox configuration in tests/e2e/setup/001-npm-sandbox.ts to include a 10-second network timeout and prefer offline mode. The reviewer suggests increasing the network timeout to 15 seconds to prevent potential test flakiness in CI environments.