Release main-d9fd108

Fix: Restore decimal precision in summary MHz values (#32)

## Summary

The benchmark summary table and JSON output were truncating MHz values
to whole numbers (e.g., `20` instead of `20.596`). This was caused by
the `BenchSummary` struct fields being `u32` with explicit `as u32`
casts in `get_bench_summary()`.

## Changes

- Changed all `BenchSummary` MHz fields from `u32` → `f64` (and
`Option<u32>` → `Option<f64>`)
- Removed the `as u32` truncating casts in both branches of
`get_bench_summary()`

## Before

```
│ Exec Min MHz     │ 18 │
│ Exec Avg MHz     │ 20 │
│ Prove Min MHz    │  1 │
```

## After

```
│ Exec Min MHz     │ 18.807 │
│ Exec Avg MHz     │ 20.487 │
│ Prove Min MHz    │ 1.874  │
```

Closes #31