[alexanto]

extracting the i/o from the api_client as transport. this is the first step towards a custom HTTP transport.
so far really just refactoring, and RequestsTransport is going to be the default transport implementation for the sync client

[Copilot]

🟡 Changes recommended

Transport-contract gaps break ETag caching, raise unexpectedly after retry exhaustion, corrupt non-UTF-8 feature data, and allow injected network failures to bypass metric restoration or abort initialization.

4 open issues

• Normalize injected response headers for case-insensitive ETag lookup · New
• Return the final response after retry exhaustion · New
• Preserve response encoding when decoding JSON · New
• Handle transport-neutral network errors in both POST methods · New

What changed in this PR

Extracts HTTP I/O from the synchronous API client into a transport layer, preparing the SDK for custom transports while keeping RequestsTransport as the default.

Changes:

• Adds request and response models, a transport protocol, and a requests-based implementation.
• Routes feature fetching, registration, and metrics submission through the transport.
• Adds tests for transport injection, request handling, retries, and session isolation.

File	Description
UnleashClient/​_unleash_api_client.py	Delegates HTTP calls to an injectable transport and interprets its responses.
UnleashClient/​_transport.py	Defines transport interfaces and the default requests implementation.
tests/​unit_tests/​test_unleash_api_client.py	Tests transport delegation for all three API operations.
tests/​unit_tests/​test_transport.py	Tests request forwarding, responses, retries, errors, and session isolation.

_{Review effort: Balanced}