feat(uv-env): add plugin for Astral's uv (#13914)

* feat(uv-env): create plugin

This plugin automatically activates/deactivates a uv-managed virtual
environment when you cd into or out of a project directory. It looks
for pyproject.toml and uv.lock to detect a uv project, and reads
UV_PROJECT_ENVIRONMENT to support custom venv locations.

* fix(uv-env): address review feedback from robbyrussell

- Add `local` to venv_dir to prevent leaking into user's shell
- Replace `export` with `typeset -g` for uv_active and uv_dir
- Use `autoload -Uz` to match the style guide

plugins/uv-env/README.md

@@ -0,0 +1,10 @@
+# uv Environment Plugin
+
+This plugin automatically activates the uv virtual environment when you cd into a project directory, and deactivates it when you cd out.
+Note: Script looks for pyproject.toml and uv.lock files to determine if it's a uv project
+
+To use it, add `uv-env` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... uv-env)
+```