docs: fix docstring inaccuracies and update outdated LangSmith URLs (#35283)
Fix several docstring inaccuracies in langchain-core and update outdated
LangSmith URLs across three README files.
**Docstring fixes (libs/core):**
- `tap_output_iter`: docstring says "async iterator" but method accepts
sync `Iterator`
- `agenerate_from_stream`: docstring says "Iterator" but method accepts
`AsyncIterator`
- `BaseLLM.OutputType`: docstring says "input type" but property returns
output type
- Grammar: "or deprecated" → "or be deprecated", "relies" → "rely",
"whose the" → "whose"
**URL fixes (libs/core, libs/langchain, libs/langchain_v1):**
- Updated `smith.langchain.com` → `www.langchain.com/langsmith` (root
README already uses the correct URL)
Verified with `make lint` and `make format` in libs/core — no new issues
introduced. Changes are docs-only with no code logic impact.
*This PR was created with assistance from an AI coding tool.*