fix(turbopack): Fix a panic when the generated hash is too short when radix formatting a string. (#80966)
## Fix hash length check in metadata formatting
### What?
Fixed a panic in the `format_radix` function when the generated hash is
shorter than 6 characters.
### Why?
The current implementation always tries to take the first 6 characters
of the hash using a fixed slice `result[..6]`, which would panic if the
hash is shorter than 6 characters. This doesn't match the JavaScript
behavior where `toString(36).slice(0, 6)` automatically takes the
minimum of the hash length and 6.
### How?
Added a check to determine the minimum length between the hash length
and 6, then use that value for slicing:
```rust
let len = result.len().min(6);
result[..len].iter().collect()
```
Fixes #PACK-4495