fix(tests): use bundled iOS TestApp instead of downloading it from github.com

[Dor-bl]

Related issue

n/a

List of changes

• Apps helper: when tests start Appium locally, use the TestApp.app.zip checked into the repo (now copied to the build output). Remote Appium servers still receive the URL.
• Apps are resolved lazily per key, so a test only fetches the app it uses. Previously the first Apps.Get downloaded every app, so a failed iOS download also failed all Android tests.
• Downloads are retried up to 4 times with exponential backoff.
• New AppsHelperTest, added to the unit-test filter in unit-test.yml and AGENTS.md.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change that adds functionality or value)
• Refactoring (non-breaking change that improves code without altering functionality)
• Breaking change (fix or feature that would cause existing functionality not to work as expected)
• New test coverage (non-breaking change that adds tests for existing, previously untested functionality)
• Test fix (non-breaking change that improves test stability or correctness)
• Chore/Maintenance (updates to build scripts, dependencies, or GitHub Actions)

Tests

• Unit tests
• Integration tests
• No automated tests (explain why below)

How they run: AppsHelperTest is added to the existing unit-test filter, so it runs on every PR (net8.0 on Windows/Linux/macOS, net48 on Windows). It runs locally on net8.0 and net48 and passes. The functional suites run on this PR's CI and are the real check of the fix. I could not run them locally because I have no emulator or simulator here.

Documentation

• Have you proposed a file change/PR with Appium to update documentation?
• Not applicable (no user-facing behaviour change, e.g. tests, CI or maintenance only)

Details

Since 2026-10-02, every Functional Tests run (including main) fails in OneTimeSetUp with:

Failed to download https://github.com/appium/dotnet-client/blob/main/test/integration/apps/archives/TestApp.app.zip?raw=true
 ----> HttpRequestException : Response status code does not indicate success: 503 (Service Unavailable).

The URL works outside GitHub Actions, so github.com appears to reject these requests from runners. This blocks the open Dependabot PRs (#1113, #1115, #1123, #1137).

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