Add runFlow timeout with context propagation

[omnarayan]

Summary

• Add timeout parameter to runFlow steps (milliseconds) that propagates into driver polling loops via SetContext(ctx), enabling mid-operation cancellation when the timeout expires
• All drivers updated: uiautomator2, wda, appium, devicelab, flutter, mock
• Informative error messages show timeout value, flow file, and which step was executing
• Timeout failures classified as TIMEOUT error type in HTML, JUnit, and Allure reports

Example usage

- runFlow:
    file: common/login.yaml
    timeout: 5000       # 5 second timeout
    env:
      username: devicelab

- runFlow:
    timeout: 3000       # inline steps with timeout
    commands:
      - tapOn: "Submit"
      - assertVisible: "Success"

Error messages

runFlow 'common/login.yaml' timed out (2s timeout)
runFlow timed out (3s timeout) while executing: assertVisible: text="THIS_ELEMENT_DOES_NOT_EXIST"
element "Username" not found: runFlow timeout (2s) exceeded

Test plan

• 4 executor unit tests + 2 parser unit tests
• Validated on real Android device (Pixel 4a) — 20 flows, 18 pass, 2 expected timeout failures
• Validated on iOS simulator (iPhone 16 Pro) — 20 flows, 14 pass, 2 expected timeout failures + 4 pre-existing iOS test issues
• No regressions in existing test suites

Ref #29 — Thanks to @maraujop for the suggestion!