#25555 [rust-axum] fix: support range response status codes (4XX, 5XX)

based on https://github.com/OpenAPITools/openapi-generator/pull/25294 with resolved merge conflicts

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Summary by cubic

Fixes the rust-axum generator so range status codes like 4XX and 5XX are sent as the concrete status chosen by the implementation instead of being dropped or replaced at the call site.

Previously the selectable status ended up emitting a fixed code and relied on body.code.parse(). Now each range response variant carries a status: u16 field, and the generated server applies it with StatusCode::from_u16, returning a 500 when the value is invalid. The change covers empty, JSON, and SSE responses, and applies all headers attached to the range response.