Remove UNC prefixes on Windows (#1086)
## Summary
This PR adds a `NormalizedDisplay` trait that we can use for user-facing
paths, to strip the UNC prefix on Windows.
On other platforms, the implementation is a no-op (vs. `Display`).
I audited all usages of `.display()`, and changed any that were
user-facing, either via `println!` or `eprintln!`, or by way of being
included in error messages. I did _not_ change uses that were only in
tests or only went to tracing.
Closes https://github.com/astral-sh/puffin/issues/1084.
