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
```

python/uv/__main__.py

@@ -0,0 +1,39 @@
+import os
+import sys
+import sysconfig
+
+
+def find_uv_bin() -> str:
+    """Return the uv binary path."""
+
+    uv_exe = "uv" + sysconfig.get_config_var("EXE")
+
+    path = os.path.join(sysconfig.get_path("scripts"), uv_exe)
+    if os.path.isfile(path):
+        return path
+
+    if sys.version_info >= (3, 10):
+        user_scheme = sysconfig.get_preferred_scheme("user")
+    elif os.name == "nt":
+        user_scheme = "nt_user"
+    elif sys.platform == "darwin" and sys._framework:
+        user_scheme = "osx_framework_user"
+    else:
+        user_scheme = "posix_user"
+
+    path = os.path.join(sysconfig.get_path("scripts", scheme=user_scheme), uv_exe)
+    if os.path.isfile(path):
+        return path
+
+    raise FileNotFoundError(path)
+
+
+if __name__ == "__main__":
+    uv = os.fsdecode(find_uv_bin())
+    if sys.platform == "win32":
+        import subprocess
+
+        completed_process = subprocess.run([uv, *sys.argv[1:]])
+        sys.exit(completed_process.returncode)
+    else:
+        os.execvp(uv, [uv, *sys.argv[1:]])