Rename to uv (#1302)

First, replace all usages in files in-place. I used my editor for this.
If someone wants to add a one-liner that'd be fun.

Then, update directory and file names:

```
# Run twice for nested directories
find . -type d -print0 | xargs -0 rename s/puffin/uv/g
find . -type d -print0 | xargs -0 rename s/puffin/uv/g

# Update files
find . -type f -print0 | xargs -0 rename s/puffin/uv/g
```

Then add all the files again

```
# Add all the files again
git add crates
git add python/uv

# This one needs a force-add
git add -f crates/uv-trampoline
```

crates/uv-resolver/src/pins.rs

@@ -0,0 +1,28 @@
+use rustc_hash::FxHashMap;
+
+use distribution_types::{CompatibleDist, Dist};
+use uv_normalize::PackageName;
+
+use crate::candidate_selector::Candidate;
+
+/// A set of package versions pinned to specific files.
+///
+/// For example, given `Flask==3.0.0`, the [`FilePins`] would contain a mapping from `Flask` to
+/// `3.0.0` to the specific wheel or source distribution archive that was pinned for that version.
+#[derive(Debug, Default)]
+pub(crate) struct FilePins(FxHashMap<PackageName, FxHashMap<pep440_rs::Version, Dist>>);
+
+impl FilePins {
+    /// Pin a candidate package.
+    pub(crate) fn insert(&mut self, candidate: &Candidate, dist: &CompatibleDist) {
+        self.0.entry(candidate.name().clone()).or_default().insert(
+            candidate.version().clone(),
+            dist.for_installation().dist.clone(),
+        );
+    }
+
+    /// Return the pinned file for the given package name and version, if it exists.
+    pub(crate) fn get(&self, name: &PackageName, version: &pep440_rs::Version) -> Option<&Dist> {
+        self.0.get(name)?.get(version)
+    }
+}