Add PostgreSQL data store implementation

This commit adds a new PostgreSQL-based key-value store using asyncpg
for async operations. The implementation follows the pattern established
by MongoDB and other distributed stores.

Features:
- Uses asyncpg (>=0.30.0) for native async/await operations
- Stores data in a single table with JSONB column for values
- Supports TTL via expires_at timestamps with lazy cleanup
- Implements all base store operations (get, put, delete, ttl)
- Includes optimized bulk operations using PostgreSQL's batch capabilities
- Provides collection enumeration and deletion
- Comprehensive test suite following existing patterns
- Marked as "Unstable" initially

The store supports initialization via:
- Connection pool injection
- Connection URL
- Individual connection parameters (host, port, database, etc.)

Files changed:
- Added PostgreSQLStore implementation and tests
- Updated pyproject.toml to include asyncpg dependency
- Updated README.md to document the new store

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

Co-authored-by: William Easton <strawgate@users.noreply.github.com>

Author: github-actions[bot]

README.md

@@ -8,8 +8,8 @@ This monorepo contains two libraries:
 
 ## Why use this library?
 
-- **Multiple backends**: DynamoDB, Elasticsearch, Memcached, MongoDB, Redis,
-  RocksDB, Valkey, and In-memory, Disk, etc
+- **Multiple backends**: DynamoDB, Elasticsearch, Memcached, MongoDB,
+  PostgreSQL, Redis, RocksDB, Valkey, and In-memory, Disk, etc
 - **TTL support**: Automatic expiration handling across all store types
 - **Type-safe**: Full type hints with Protocol-based interfaces
 - **Adapters**: Pydantic model support, raise-on-missing behavior, etc
@@ -123,7 +123,7 @@ pip install py-key-value-aio[memory]
 pip install py-key-value-aio[disk]
 pip install py-key-value-aio[dynamodb]
 pip install py-key-value-aio[elasticsearch]
-# or: redis, mongodb, memcached, valkey, vault, registry, rocksdb, see below for all options
+# or: redis, mongodb, postgresql, memcached, valkey, vault, registry, rocksdb, see below for all options
 ```
 
 ```python
@@ -231,6 +231,7 @@ system, for access across multiple application nodes.
 | Elasticsearch    | Unstable | ✅  |  ✅  | `ElasticsearchStore(url="https://localhost:9200", api_key="your-api-key", index="kv-store")` |
 | Memcached        | Unstable | ✅  |  ✖️   | `MemcachedStore(host="127.0.0.1", port=11211")` |
 | MongoDB          | Unstable | ✅  |  ✅  | `MongoDBStore(url="mongodb://localhost:27017/test")` |
+| PostgreSQL       | Unstable | ✅  |  ✖️   | `PostgreSQLStore(url="postgresql://localhost:5432/mydb")` |
 | Redis            | Stable | ✅  |  ✅  | `RedisStore(url="redis://localhost:6379/0")` |
 | Valkey           | Stable | ✅  |  ✅  | `ValkeyStore(host="localhost", port=6379)` |
 

key-value/key-value-aio/pyproject.toml

@@ -36,6 +36,7 @@ memory = ["cachetools>=5.0.0"]
 disk = ["diskcache>=5.0.0", "pathvalidate>=3.3.1",]
 redis = ["redis>=4.3.0"]
 mongodb = ["pymongo>=4.0.0"]
+postgresql = ["asyncpg>=0.30.0"]
 valkey = ["valkey-glide>=2.1.0"]
 vault = ["hvac>=2.3.0", "types-hvac>=2.3.0"]
 memcached = ["aiomcache>=0.8.0"]
@@ -67,7 +68,7 @@ env_files = [".env"]
 
 [dependency-groups]
 dev = [
-    "py-key-value-aio[memory,disk,redis,elasticsearch,memcached,mongodb,vault,dynamodb,rocksdb]",
+    "py-key-value-aio[memory,disk,redis,elasticsearch,memcached,mongodb,postgresql,vault,dynamodb,rocksdb]",
     "py-key-value-aio[valkey]; platform_system != 'Windows'",
     "py-key-value-aio[keyring]",
     "py-key-value-aio[pydantic]",

key-value/key-value-aio/src/key_value/aio/stores/postgresql/__init__.py

@@ -0,0 +1,9 @@
+"""PostgreSQL store for py-key-value-aio."""
+
+try:
+    from key_value.aio.stores.postgresql.store import PostgreSQLStore
+except ImportError as e:
+    msg = "PostgreSQLStore requires py-key-value-aio[postgresql]"
+    raise ImportError(msg) from e
+
+__all__ = ["PostgreSQLStore"]