Use traceable context (#11896)
Example
```
from langchain.schema.runnable import RunnableLambda
from langsmith import traceable
chain = RunnableLambda(lambda x: x)
@traceable(run_type = "chain")
def my_traceable(a):
chain.invoke(a)
my_traceable(5)
```
Would have a nested result.
This would NOT work for interleaving chains and traceables. E.g., things
like thiswould still not work well
```
from langchain.schema.runnable import RunnableLambda
from langsmith import traceable
@traceable()
def other_traceable(a):
return a
def foo(x):
return other_traceable(x)
chain = RunnableLambda(foo)
@traceable(run_type = "chain")
def my_traceable(a):
chain.invoke(a)
my_traceable(5)
```
