feat: responses & crate ergonomics + bug fixes

[64bit]

• add From trait to improve ergonomics for Responses API types - this prevent having to write nested enums ; or structs with just one field - by simily using .into()
• implement EventType for Responses streaming events
• Fixed and closes Responses API streaming response.function_call_arguments.done event missing function name #472
• Fixed and closes Event source StreamEnded handling #456
• Fixes types whose fields were not public
• Add new responses api examples to test all of the above.
• introduce form.rs, impls.rs, sdk.rs for each type module, introduce impls.rs for group-api wrapper types