feat: Add LangGraph integration

[shellmayr]

• Add LangGraph integration
• Compilation of StateGraphs results in an agent creation span (according to OTEL semantic conventions)
• Runtime executions are done on Pregel instances - we are wrapping their invoke & ainvoke which produces the invoke_agent spans
• There's some internals that automatically switch between invoke & stream on CompiledStateGraph (which is a subclass of Pregel), which results in duplicate spans if both are instrumented. For now, only invoke is wrapped to prevent this duplication.
• Agent handoffs in LangGraph are done via tools - so there is no real possibility to create handoff spans within the SDK. Looks like this will be handled in product logic instead.

Closes TET-991
Closes PY-1799

[linear]

TET-991 Add integration for langgraph

[codecov]

Codecov Report

❌ Patch coverage is 76.75676% with 43 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.75%. Comparing base (c378c2d) to head (f903562).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
sentry_sdk/integrations/langgraph.py	76.63%	18 Missing and 25 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #4727       +/-   ##
===========================================
+ Coverage   73.15%   84.75%   +11.60%     
===========================================
  Files         157      158        +1     
  Lines       16138    16323      +185     
  Branches     2744     2792       +48     
===========================================
+ Hits        11805    13835     +2030     
+ Misses       3640     1672     -1968     
- Partials      693      816      +123     

Files with missing lines	Coverage Δ
sentry_sdk/consts.py	99.33% <100.00%> (+<0.01%)	⬆️
sentry_sdk/integrations/__init__.py	87.01% <ø> (ø)
sentry_sdk/integrations/langgraph.py	76.63% <76.63%> (ø)

... and 40 files with indirect coverage changes

[linear]

BE-532 Langgraph integration to sentry

PY-1799 Add integration for `langgraph`

[antonpirker]

Now its ready to be merge. Thanks for the great work @shellmayr !