Merge pull request #10 from modern-python/story/2-3-request-immutability-helpers

feat(story-2.3): Request/Response immutability helper expansion

Author: lesnik512

CHANGELOG.md

@@ -21,5 +21,6 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 - `ResponseDecoder` protocol (`@runtime_checkable`) and default `PydanticDecoder` adapter — single-parse-pass JSON decoding via `pydantic.TypeAdapter.validate_json(bytes)`; a module-level `@functools.lru_cache(maxsize=None)` factory (`_get_adapter`) memoizes one `TypeAdapter` per `response_model` across the process so warm-path requests pay zero adapter-construction cost; `pydantic.ValidationError` surfaces unchanged to the caller (Story 1.5).
 - `Middleware` protocol (`@runtime_checkable`) and `Next` callable type alias (`Callable[[Request], Awaitable[Response]]`); private `compose(middlewares, transport)` chain composer at `httpware._internal.chain` using a recursive closure fold with `transport.__call__` as the bottom of the chain. No exception handling inside `compose`, so `asyncio.CancelledError` and user-raised exceptions propagate untouched (Story 2.1).
 - Phase-shortcut decorators `@before_request`, `@after_response`, `@on_error` for lifecycle hooks without authoring a full `Middleware` class. `@on_error` catches `Exception` only (so `asyncio.CancelledError` propagates); its handler may return a `Response` to recover or `None` to re-raise (Story 2.2).
+- Request and Response immutability helper expansion: `Request.with_headers`, `with_cookie`, `with_cookies`, `with_extension`, `with_extensions`; `Response.with_headers`, `with_status`. Plural helpers merge mappings (incoming keys override existing); singular helpers add or replace a single entry. No validation, no header-key normalization — matches the existing `with_header` semantics from Story 1.2 (Story 2.3).
 
 [Unreleased]: https://github.com/modern-python/httpware/commits/main