Document transport options and add requests extra

Expand README with an optional HTTP transport section detailing the transport abstraction, how to use the built-in RequestsTransport (multisafepay[requests]) or provide a custom transport, and a small example. Update example import to use from multisafepay import Sdk. Tweak RequestsTransport's ModuleNotFoundError message to also suggest installing requests directly. Update poetry.lock to reflect the new optional extra and lockfile checksum.

Author: zulquer

README.md

@@ -20,18 +20,57 @@ your transactions in one place!
 
 ## Installation
 
-Here's how to use pip to put the MultiSafepay library into your Python.
+If you want to use the built-in default transport, install with the `requests` extra.
+
+```bash
+pip install "multisafepay[requests]"
+```
+
+If you want to provide your own transport implementation, install the base package.
+
+```bash
+pip install multisafepay
+```
+
+## HTTP client / transport (optional dependency)
+
+**WARNING:** This SDK does not have a hard dependency on a specific HTTP client.
+
+The SDK uses a small transport abstraction so you can choose (and swap) the underlying HTTP implementation without affecting the rest of your integration.
+
+### How it works
+
+- The SDK expects an object implementing the `HTTPTransport` / `HTTPResponse` protocols defined in `src/multisafepay/transport/http_transport.py`.
+- If you do not provide a transport, the SDK defaults to `RequestsTransport`.
+- `requests` is an optional extra:
+    - To use the default transport, install `multisafepay[requests]`.
+    - To avoid `requests`, inject your own transport (for example, `httpx` or `urllib3`).
+
+### Custom transport example
 
 ```bash
 pip install multisafepay
 ```
 
+```python
+from multisafepay import Sdk
+
+
+sdk = Sdk(
+    api_key="<api_key>",
+    is_production=False,
+    transport=my_custom_transport,  # must implement HTTPTransport
+)
+```
+
+See transport examples in `examples/transport/` (`httpx_transport.py`, `urllib3_transport.py`, `request_transport.py`).
+
 ## Getting started
 
 ### Initialize the client
 
 ```python
-from multisafepay.sdk import Sdk
+from multisafepay import Sdk
 
 multisafepay_sdk: Sdk = Sdk(api_key='<api_key>', is_production=True)
 ```

poetry.lock

@@ -34,7 +34,7 @@
 def _raise_requests_missing() -> None:
     raise ModuleNotFoundError(
         "Optional dependency 'requests' is required for RequestsTransport. "
-        "Install it via 'pip install multisafepay[requests]' (or add the Poetry extra 'requests'), "
+        "Install it via 'pip install multisafepay[requests]' or 'pip install requests', "
         "or pass a custom HTTPTransport implementation to Sdk(..., transport=...).",
     ) from _REQUESTS_IMPORT_ERROR