feat(repopo): Add Cargo workspace policies for Rust monorepos

[tylerbutler]

Summary

Add policies for Cargo workspace management in Rust monorepos.

Proposed Policies

WorkspaceMembersValid

Validate workspace configuration:

makePolicy(WorkspaceMembersValid, {
  validatePaths: true,         // All members paths must exist
  detectOrphans: true,         // Find crates not in workspace
  requireExplicitMembers: true, // Prefer explicit over glob patterns
})

SharedDependencyVersions

Enforce consistent dependency versions across workspace:

makePolicy(SharedDependencyVersions, {
  // Require workspace-level dependencies
  requireWorkspaceDeps: ["serde", "tokio", "anyhow"],
  
  // Detect version mismatches
  detectMismatches: true,
  
  // Suggest workspace.dependencies for duplicates
  suggestWorkspaceDeps: true,
})

WorkspaceInheritance

Ensure members inherit from workspace:

makePolicy(WorkspaceInheritance, {
  // Fields that should use workspace inheritance
  inherit: ["version", "authors", "license", "repository"],
  
  // Allow overrides for specific crates
  allowOverrides: ["examples/*"],
})

Use Case

Large Rust monorepos with multiple crates benefit from consistent workspace configuration and dependency management.

Related

This complements the existing monorepo support in repopo for Node.js workspaces.