Index out of bounds error in `quantile_duration` in src/results.rs

**Describe the bug**
An "index out of bounds" error occurs in `src/results.rs` during benchmark runs. The error message `index out of bounds: the len is 1 but the index is 1` at `src/results.rs:252:31` points to an issue in the `quantile_duration` function.

**To Reproduce**
Steps to reproduce the behavior:
1. Run a benchmark with settings that might result in only one successful response.
2. Observe the panic.

**Expected behavior**
The `quantile_duration` function should handle cases where the `data` vector has only one element, possibly by returning that single element or a predefined value, instead of panicking.

**Console logs**
```
export URL = http://localhost:8000/v1
sudo docker run --network host \
-e HF_TOKEN=$HF_TOKEN \
-v ~/inference-benchmarker-results:/opt/inference-benchmarker/results \
inference_benchmarker inference-benchmarker \
--prompt-options "num_tokens=200,max_tokens=220,min_tokens=180,variance=10" \
--decode-options "num_tokens=200,max_tokens=220,min_tokens=180,variance=10"
--url $URL
...
thread 'tokio-runtime-worker' panicked at /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/ratatui-0.29.0/src/terminal/init.rs:52:16:
thread 'tokio-runtime-worker' panicked at src/results.rs:252:31:chmarker/src/event.rs:40:48:cf8c6b5b557f/ratatui-0.29.0/src/terminal/init
index out of bounds: the len is 1 but the index is 1ailed to initialize input reader" }
```

**Possible Cause**
The `quantile_duration` function at `src/results.rs:252` accesses `data[i as usize + 1]` without checking if `i as usize + 1` is a valid index. If `data` has only one element, and `i` is 0 (which can happen if `quantile` is such that `(data.len() - 1) as f64 * quantile` is less than 1), then `i as usize + 1` would be 1, leading to an out-of-bounds access.

**Suggested Fix**
Add a check within the `quantile_duration` function to handle cases where the length of the `data` vector is 1, or when `i as usize + 1` would be out of bounds. For example, if `data.len()` is 1, the function could return `data[0].as_secs_f64()`.

**Environment:**
- OS: Ubuntu 24 LTS as WSL with Windows 11 host
- inference-benchmarker version: build `inference_benchmarker:latest` from `2025-05-15T18:48:42.880472539+02:00`

**Remark**
this issue was created with the help of Gemini 2.5 Pro (especially the parts about possible cause and suggested fix...)