[opentelemetry-instrumentation-google-genai] Add response id attribute, cleanup dictutil code

[DylanRussell]

Description

Add response id attribute to inference span and completion event for Google GenAi...

See https://opentelemetry.io/docs/specs/semconv/gen-ai/gen-ai-spans/

I also drastically cleaned up the dict_util code which converts the GenerateContentConfig object into OTEL Attributes dictionary.. I deleted some unused functionality and cleaned up the code.

Type of change

• [ x] New feature (non-breaking change which adds functionality)

How has this been tested?

Unit tests

Checklist

See CONTRIBUTING.md
for the style guide, changelog guidance, and more.

• [x ] Followed the style guidelines of this project
• Changelog updated if the change requires an entry
• [ x] Unit tests added
• [ x] Documentation updated

[Copilot]

Pull request overview

Adds gen_ai.response.id propagation for Google GenAI generate_content so the response id can be attached to the inference span and the completion event, aligning with the GenAI semantic conventions.

Changes:

• Extract response_id from GenerateContentResponse and attach it to the util-genai InferenceInvocation.
• Update non-streaming tests to assert gen_ai.response.id presence/absence on spans/events.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
instrumentation/opentelemetry-instrumentation-google-genai/src/opentelemetry/instrumentation/google_genai/generate_content.py	Captures response attributes (including response id) into the invocation for span/event emission.
instrumentation/opentelemetry-instrumentation-google-genai/tests/generate_content/nonstreaming_base.py	Adds non-streaming assertions validating the gen_ai.response.id attribute behavior.

[DylanRussell]

@eternalcuriouslearner @lmolkova mind taking another look ? Ended up doing a bunch of code cleanup after noticing some messy code here..

[DylanRussell]

The failing tests In the CI will be fixed by #117 and or #133

[DylanRussell]

I think this PR should be good to be merged now