Problem

ctx.Status(code) doesn't flush the status code to the underlying http.ResponseWriter when no body is written. This causes httptest.ResponseRecorder and similar wrappers to see the default 200 instead of the actual status code.

recorder := httptest.NewRecorder()
c, _ := gin.CreateTestContext(recorder)
c.Status(http.StatusNoContent)
fmt.Println(recorder.Code) // 200 — should be 204

Reported in #4071.

Root Cause

ctx.Status() calls c.Writer.WriteHeader(code), which only stores the status in gin's responseWriter buffer. The status gets flushed to the underlying writer when Write() is called (which triggers WriteHeaderNow()). But for status codes that never have a body (1xx, 204, 304), no Write() ever happens, so the status never reaches the underlying ResponseRecorder.

This is inconsistent with ctx.Render(), which already calls WriteHeaderNow() for no-body status codes.

Fix

When Status() is called with a no-body status code (where bodyAllowedForStatus() returns false), immediately flush the status to the underlying writer via WriteHeaderNow(). This mirrors the existing behavior in Render() and matches user expectations.

For status codes that allow a body (e.g. 200), Status() continues to buffer the status until Write() is called, preserving the existing behavior for handlers that set a status before writing content.

Tests

• TestContextStatusFlushesNoBodyCodes: verifies 100, 101, 102, 204, and 304 flush immediately
• TestContextStatusWithBodyDoesNotFlushEarly: verifies 200 still buffers until Write() is called

All existing tests continue to pass.

Fixes #4071