Add spellchecker to pre-commit hooks

Adds typos spellchecker to catch common spelling errors while
respecting project-specific terminology like LangChain async
method names and gitignore patterns.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: abrookins

.pre-commit-config.yaml

@@ -15,3 +15,9 @@ repos:
       - id: end-of-file-fixer
       - id: check-yaml
       - id: check-added-large-files
+
+  - repo: https://github.com/crate-ci/typos
+    rev: v1.16.26
+    hooks:
+      - id: typos
+        args: [--config, _typos.toml]

_typos.toml

@@ -0,0 +1,8 @@
+[default.extend-words]
+# LangChain async method names - not typos
+aadd = "aadd"
+# Gitignore patterns - not typos
+nclude = "nclude"
+
+[files]
+extend-exclude = ["tests/fixtures/"]