fix(langchain): add missing section on handling tool errors

[christian-bromann]

The section was missing examples.

[github-actions]

Mintlify preview ID generated: preview-cbhand-1764049439-3312c89

[eyurtsev]

This should have a comment saying something conceptually about what kind of errors need to be retried by an LLM.

There are at least 4 types of errors:

1. network failures (should be handeled using tool retry middleware)
2. incorrect tool implementation (should bubble up)
3. llm invocation errors that arise from a schema mismatch -- already auto-handeled!
4. llm invocation errors that happen somewhere inside the function (e.g., def execute_sql(sql: str) -> str was invoked with sql="hello world". sql is a string (so won't raise an exception from schema mismatch, but will raise an error later on due to the sql being invalid sql! <-- This is the only type of error that should be handled this way