Add value hints to command line arguments to improve shell completion accuracy (#17080)

## Summary

This partially addresses #17076 by adding `value_hint` to various
arguments.

For cases where an option takes a path to either specifically a file or
a directory directory, `ValueHint::FilePath` and `ValueHint::DirPath`
are used respectively to try to limit the amount of noise presented by
completions in shells which support it.

For cases where a URL (and only a URL, not a path) can be supplied,
`ValueHint::Url` is used.

For cases where a python interpreter is to be specified,
`ValueHint::CommandName` is used which will tab complete from `$PATH` by
default, but will fall back to completing executable filenames if you
start typing a path.

Finally, for the many cases where there is no built in completion which
would make sense, and where default completion of a path would make no
sense (e.g. a package name, or version specifier, or date)
`ValueHint::Other` is used to explicitly disable completion.

## Test Plan

Manually tested a bunch of these. These _could_ be automated in the
sense that we could snapshot the completion from zsh but I've not
thought about how that could be done yet.

crates/uv-cache/src/cli.rs

@@ -3,7 +3,7 @@ use std::path::{Path, PathBuf};
 use uv_static::EnvVars;
 
 use crate::Cache;
-use clap::Parser;
+use clap::{Parser, ValueHint};
 use tracing::{debug, warn};
 
 #[derive(Parser, Debug, Clone)]
@@ -27,7 +27,7 @@ pub struct CacheArgs {
     /// `%LOCALAPPDATA%\uv\cache` on Windows.
     ///
     /// To view the location of the cache directory, run `uv cache dir`.
-    #[arg(global = true, long, env = EnvVars::UV_CACHE_DIR)]
+    #[arg(global = true, long, env = EnvVars::UV_CACHE_DIR, value_hint = ValueHint::DirPath)]
     pub cache_dir: Option<PathBuf>,
 }