feat(langgraph): Response model attribute on invocation spans

[alexander-alderman-webb]

Description

Add the last response model name to LangGraph invocation spans.

Issues

Contributes to #5170

Reminders

• Please add tests to validate your changes, and lint your code using tox -e linters.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.23%. Comparing base (4f3fab3) to head (5eb9a9a).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@                   Coverage Diff                    @@
##           webb/langgraph-major    #5212      +/-   ##
========================================================
+ Coverage                 84.22%   84.23%   +0.01%     
========================================================
  Files                       181      181              
  Lines                     18486    18476      -10     
  Branches                   3295     3292       -3     
========================================================
- Hits                      15569    15563       -6     
+ Misses                     1899     1896       -3     
+ Partials                   1018     1017       -1     

Files with missing lines	Coverage Δ
sentry_sdk/integrations/langgraph.py	77.33% <100.00%> (+1.05%)	⬆️

... and 2 files with indirect coverage changes