Add `gen_ai.request.stop_sequences` attribute

[ericapisani]

Problem

OTel GenAI semconv recommends capturing gen_ai.request.stop_sequences (string[]). Google's GenerateContentConfig has a stop_sequences parameter, but it is not captured by the integration.

Context

Other config parameters (temperature, top_p, top_k, max_output_tokens, presence_penalty, frequency_penalty, seed) are already captured in the param loop at utils.py:834-846. Adding stop_sequences follows the same pattern.

Files

• sentry_sdk/integrations/google_genai/utils.py — set_span_data_for_request()
• sentry_sdk/consts.py — may need a new SPANDATA constant if one doesn't exist

Acceptance Criteria

• stop_sequences from GenerateContentConfig is captured on the span
• Test added to verify the attribute is set when stop_sequences is provided

[linear-code]

PY-2219

[alexander-alderman-webb]

Not in the RFC today: getsentry/rfcs#153