feat: Python 3.14 compatibility, connection retry resilience, ParsingError, raw client improvements

[fern-api]

Changes

Python 3.14 Compatibility

• Removed pydantic.v1 imports in core/pydantic_utilities.py - replaced with stdlib typing equivalents (get_args, get_origin, is_literal_type, is_union) and inlined encoders_by_type to avoid deprecated Pydantic v1 compatibility layer that breaks on Python 3.14

Connection Retry Resilience

• HttpClient and AsyncHttpClient now retry on httpx.ConnectError and httpx.RemoteProtocolError (transient network failures), not just HTTP status codes
• New _retry_timeout_from_retries() for exponential backoff when no response is available
• Configurable base_max_retries parameter on both clients
• Fixed missing data and force_multipart parameters in retry call paths (previously dropped on retry)

New: ParsingError Exception

• Added core/parse_error.py with ParsingError class - raised when server responses fail Pydantic validation, wrapping the original ValidationError as cause
• All raw_client.py files now catch ValidationError and raise ParsingError with status code, headers, and body context

New: RFC 2822 DateTime Support

• Added Rfc2822DateTime type and parse_rfc2822_datetime helper in core/datetime_utils.py
• Supports parsing RFC 2822 date strings (e.g., "Wed, 02 Oct 2002 13:00:00 GMT") with ISO 8601 fallback

AsyncAuth0 Improvements

• New async_token parameter for async token acquisition (e.g., refreshing tokens via async HTTP client)
• Auto-detection of httpx_aiohttp via _make_default_async_client() - uses aiohttp transport when available, falls back to httpx.AsyncClient
• New _default_clients.py module with DefaultAioHttpClient and DefaultAsyncHttpxClient

Raw Client Updates

• Replaced jsonable_encoder with encode_path_param for URL path encoding across all raw clients
• Added ParsingError handling to all error response paths

Type & Documentation Changes

• 346 type files updated (new types, field additions, docstring improvements)
• Updated reference.md API documentation
• Expanded wiremock-mappings.json with additional test fixtures