Avoid canonicalizing user-provided interpreters (#2072)

## Summary

We shouldn't be resolving symlinks on the provided interpreter;
otherwise we break `pyenv`, since running `cargo run pip install mypy
--python .venv/bin/python` will immediately resolve to (e.g.)
`/Users/crmarsh/.pyenv/versions/3.10.2/bin/python3.10`, and pyenv relies
on the path to do its lookups.

Instead, the canonicalizing happens when we query the interpreter
metadata.

Closes https://github.com/astral-sh/uv/issues/2068.

## Test Plan

Ran `cargo run pip install mypy --python .venv/bin/python -v -n` with a
virtualenv created using a pyenv Python; verified that Mypy was
installed into the virtual environment, rather than into the global
environment.

crates/uv-fs/src/path.rs

@@ -1,5 +1,5 @@
 use std::borrow::Cow;
-use std::path::Path;
+use std::path::{Component, Path, PathBuf};
 
 pub trait Simplified {
     /// Simplify a [`Path`].
@@ -46,6 +46,36 @@ pub fn normalize_url_path(path: &str) -> Cow<'_, str> {
     }
 }
 
+/// Normalize a path, removing things like `.` and `..`.
+///
+/// Source: <https://github.com/rust-lang/cargo/blob/b48c41aedbd69ee3990d62a0e2006edbb506a480/crates/cargo-util/src/paths.rs#L76C1-L109C2>
+pub fn normalize_path(path: impl AsRef<Path>) -> PathBuf {
+    let mut components = path.as_ref().components().peekable();
+    let mut ret = if let Some(c @ Component::Prefix(..)) = components.peek().copied() {
+        components.next();
+        PathBuf::from(c.as_os_str())
+    } else {
+        PathBuf::new()
+    };
+
+    for component in components {
+        match component {
+            Component::Prefix(..) => unreachable!(),
+            Component::RootDir => {
+                ret.push(component.as_os_str());
+            }
+            Component::CurDir => {}
+            Component::ParentDir => {
+                ret.pop();
+            }
+            Component::Normal(c) => {
+                ret.push(c);
+            }
+        }
+    }
+    ret
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;