deps: add missing dependencies in test group (#223)

This PR adds missing dependencies to `pyproject.toml` test dependency
group (used for local development).
Added dependencies:

- `codespell` - required to run `make spell_check` and `make spell_fix`
scripts
- `pytest-watcher` - required to run `make test_watch`
- `greenlet` - without it, `make test` fails with error below. It was
previously added in #161, but lost at some point.
```
ValueError: the greenlet library is required to use this function. No module named 'greenlet'
```

Author: nazarpechka

pyproject.toml

@@ -13,7 +13,7 @@ dependencies = [
     "pgvector>=0.2.5,<0.4",
     "psycopg>=3,<4",
     "psycopg-pool>=3.2.1,<4",
-    "sqlalchemy>=2,<3",
+    "sqlalchemy[asyncio]>=2,<3",
     "numpy>=1.21,<3",
 ]
 
@@ -22,6 +22,7 @@ dependencies = [
 
 [dependency-groups]
 test = [
+    "codespell>=2.4.1",
     "langchain-tests==0.3.7",
     "mypy>=1.15.0",
     "pytest>=8.3.4",
@@ -30,6 +31,7 @@ test = [
     "pytest-mock>=3.14.0",
     "pytest-socket>=0.7.0",
     "pytest-timeout>=2.3.1",
+    "pytest-watcher>=0.4.3",
     "ruff>=0.9.7",
 ]