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'
```

…riable (#243)

See #241 for reference.

---------

Co-authored-by: c.decoopman <c.decoopman@axeal.com>

Adds documentation for hybrid search

This PR adds:
- A code snippet in the README
- Section in the how-to guide on multiple scenarios the hybrid search
config can be used in. The scenarios are
      - Creating a new table with the tsv column
      - Using a pre-existing table without the tsv column
      - Hybrid search only on specific similarity searches.
      - Applying hybrid search index

See #238 for details.

Added code to expose the functions (aapply_hybrid_search_index,
apply_hybrid_search_index) for adding an index to the tsv column in
hybrid search.

I also fixed minor typos in the existing test code for better
readability.

```diff
-DEFAULT_TABLE_ASYNC = "default_sync" ...
+DEFAULT_TABLE_ASYNC = "default_async" ...
```

- `langchain_postgres/v2/vectorstores.py`: Added new index creation
methods
- `tests/unit_tests/v2/test_pg_vectorstore_index.py`: Added
comprehensive test coverage
- `pyproject.toml`: Updated test dependencies
- `tests/utils.py`: Minor updates
- `DEVELOPMENT.md`: Minor updates

It also includes changes to align test-related environment variable
settings between `DEVELOPMENT.md` and `utils.py`.

For testing, I initially attempted to use the existing dependency
`psycopg`, but on my current environment (not installed deps like libpq,
MacBook Apple M4 Max), running with the existing dependency caused
errors. To ensure compatibility across environments, I added
`psycopg[binary]`.

<details>
<summary> psycopg error </summary> 

```bash
    import_from_libpq()
.venv/lib/python3.13/site-packages/psycopg/pq/__init__.py:108: in import_from_libpq
    raise ImportError(
E   ImportError: no pq wrapper available.
E   Attempts made:
E   - couldn't import psycopg 'c' implementation: No module named 'psycopg_c'
```

</details>

---------

Co-authored-by: dishaprakash <57954147+dishaprakash@users.noreply.github.com>

This PR adds a clarification into the PGVectorStore How-To guide that
the dense vector search is the primary search and the TSV based search
is the secondary search.

Fixes Major Issue 1 in
#234

---------

Co-authored-by: Averi Kitsch <akitsch@google.com>

Fixes Major Issue 1 in
#234

---------

Co-authored-by: Averi Kitsch <akitsch@google.com>

This PR fixes the 2nd Major issue in
#234, related
to Configuration and Querying Issues

Issue breakdown:
-
**Inconsistent k Parameter:** For hybrid searches, the dense search
LIMIT was tied to the final k parameter, while the sparse search used
its own secondary_top_k.
**Late Initialization of HybridSearchConfig:** The HybridSearchConfig
was initialized after the k parameter was calculated, which could lead
to incorrect behavior if the config was passed dynamically via `kwargs`.

Overview of the changes:
-
1. The __query_collection method now uses a separate `dense_limit` for
the dense search query.
If HybridSearchConfig is active, dense_limit is set to primary_top_k.
For dense-only searches, dense_limit defaults to the final k value,
preserving the existing behavior.

2. The hybrid_search_config is now initialized at the beginning of
`__query_collection`, ensuring that any `kwargs` overrides are handled
before `k` or `dense_limit` are calculated.