docs(readme): document --speed flag in Go/Rust/Java/Swift args tables

The --speed parameter was announced in each language README's
"Update News" entry dated 2025.11.19 and is already parsed by the
example code in every language ({go,rust,java,swift}/example_onnx.*),
but the "Available Arguments" reference table is missing the row in
4 of the 8 language READMEs. The Python, Node.js, C#, and C++ READMEs
already list it.

Add the missing row in each affected table, verbatim with the wording
already used in the other 4 READMEs:

  | --speed | float | 1.05 | Speech speed factor (higher = faster, lower = slower) |

Go uses single-dash to match the surrounding rows in its own table.

swift/README.md

@@ -97,6 +97,7 @@ This will:
 | `--use-gpu` | flag | False | Use GPU for inference (default: CPU) |
 | `--onnx-dir` | str | `../assets/onnx` | Path to ONNX model directory |
 | `--total-step` | int | 8 | Number of denoising steps (higher = better quality, slower) |
+| `--speed` | float | 1.05 | Speech speed factor (higher = faster, lower = slower) |
 | `--n-test` | int | 4 | Number of times to generate each sample |
 | `--voice-style` | str+ | `../assets/voice_styles/M1.json` | Voice style file path(s) |
 | `--text` | str+ | (long default text) | Text(s) to synthesize |