[espresso] Adopt code-excerpts for README

[danielleon-cmd]

The excerpt validator (readme_validator.dart) only requires <?code-excerpt?> management for Dart code blocks, so the README's Java/Groovy/XML/sh snippets are left untouched. The one Dart block — the test_driver/ script — used the deprecated flutter_driver enableFlutterDriverExtension() API, which no longer has a real, compilable counterpart in this repo now that the example app migrated to the integration_test package. Points the excerpt at the example's actual test_driver/integration_test.dart (integrationDriver()) instead, and updates the surrounding prose and the ./gradlew command to match the real filename. Also drops the package's ci_config.yaml, whose only purpose was opting it out of that validation.

Follows the same pattern as #12641 ([pointer_interceptor] Adopt code-excerpts for README) and #12643 ([quick_actions] Adopt code-excerpts for README).

Part of #102679.

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the AI contribution guidelines and understand my responsibilities, or I am not using AI tools.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter.
• I signed the CLA. — pending; the CLA bot flagged this as a first-time contribution from this account.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I followed the version and CHANGELOG instructions, using semantic versioning and the repository CHANGELOG style (bumped to 0.4.0+26).
• I updated/added any relevant documentation (doc comments with ///). — not applicable, no public API surface changed.
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹. — documentation-only change: the updated test_driver/integration_test.dart docregion is validated by dart analyze/dart format and the update-excerpts check itself; no runtime behavior changed.
• All existing and new tests are passing.

Test plan

• dart run script/tool/bin/flutter_plugin_tools.dart update-excerpts --packages=espresso — no diff after regeneration
• dart run script/tool/bin/flutter_plugin_tools.dart validate --packages=espresso — no issues
• flutter analyze in example/ — no issues
• dart format --output=none --set-exit-if-changed on the updated driver file — no changes needed
• No Dart unit tests exist for this package (native-only bindings), so none to run

Note: The Flutter team is currently trialing Gemini Code Assist for GitHub. Comments from gemini-code-assist[bot] aren't authoritative Flutter-team feedback; I'll wait for a human reviewer's guidance on which automated comments (if any) should be addressed.

Footnotes

1. Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling. ↩

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.