[Windows] Panic in cache path tracking when a malformed observed path reaches `RelativePathBuf::clean()`

[SegaraRai]

Vite Task can panic in the cache/file-access tracking path when user code accesses a malformed path.

This is clearly a bug in user code, but Vite Task should still handle it gracefully instead of panicking.

The failure mode seems to be:

1. file access tracking observes a malformed path
2. the path is stripped relative to the workspace
3. RelativePathBuf::new(...) accepts it
4. RelativePathBuf::clean() makes it non-relative
5. Vite Task panics

A minimal example of the kind of access that triggers this on Windows is:

import fs from "node:fs";

fs.readFileSync("foo/C:/bar", "utf8");

Other path shapes that reproduce the same problem:

• file:\\C:\\bar
• foo\\file:\\C:\\bar
• foo/file:/C:/bar

The panic looks like this:

thread 'main' panicked at crates\vite_path\src\relative.rs:84:39:
cleaning a relative path preserves relativity: NonRelative

So the issue seems to be malformed observed paths that are initially accepted as relative, but become non-relative during cleanup.

Expected behavior

Even if user code touches an invalid path, Vite Task should not panic. It should skip the path, mark the task uncacheable, or return a normal error with context.