Add uv build --all option (#7724)

## Summary

Resolves #7705 

## Test Plan

`cargo test` and tested locally.

The snapshots were unstable due to the packages being built in a
non-deterministic order, so I used the quiet flag to suppress the
output.

Another question is whether we should label the build output to indicate
which package it belongs to?

crates/uv-cli/src/lib.rs

@@ -2011,9 +2011,18 @@ pub struct BuildArgs {
     /// directory if no source directory is provided.
     ///
     /// If the workspace member does not exist, uv will exit with an error.
-    #[arg(long)]
+    #[arg(long, conflicts_with("all"))]
     pub package: Option<PackageName>,
 
+    /// Builds all packages in the workspace.
+    ///
+    /// The workspace will be discovered from the provided source directory, or the current
+    /// directory if no source directory is provided.
+    ///
+    /// If the workspace member does not exist, uv will exit with an error.
+    #[arg(long, conflicts_with("package"))]
+    pub all: bool,
+
     /// The output directory to which distributions should be written.
     ///
     /// Defaults to the `dist` subdirectory within the source directory, or the