feat: add WithInvocationID run option

[quoral]

Problem:
InvocationID was not able to be set from the callers of the ADK. This did not match the adk-python implementation. This has made us not being able to follow the resume functionality within the adk-python guide here.

Solution:
This adds a RunOption that lets a caller pass an existing invocation ID into
runner.Run. When set, the invocation context uses the supplied ID
instead of generating a fresh one.

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

Please include a summary of passed go test results.

Manual End-to-End (E2E) Tests:

I have started and run our adk-go Agent with these fixes, and ensured that there are no regressions in other behaviors.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

[radhus]

@mazas-google tagging you 🙏