Add cargo ci dlls command for building C# DLLs and NuGet packages

sdks/csharp/.meta-check-ignore

@@ -0,0 +1,2 @@
+unity-meta-skeleton~
+unity-meta-skeleton~/**

sdks/csharp/packages/.gitignore

@@ -1,11 +1,15 @@
 # Ignore most of NuGet package structure, except DLLs which are required by Unity.
+/*/*
+!/*/*/
 /*/*/*
 
 !/*/*/analyzers
 !/*/*/analyzers.meta
+!/*/*/analyzers/**
 
 !/*/*/lib
 !/*/*/lib.meta
+!/*/*/lib/**
 
 # Ignore XML documentation metadata from packages too.
 *.xml

tools/ci/README.md

@@ -70,6 +70,21 @@ Usage: wasm-bindings
 
 - `--help`: Print help (see a summary with '-h')
 
+### `dlls`
+
+Builds and packs C# DLLs and NuGet packages for local Unity workflows
+
+Packs the in-repo C# NuGet packages and restores the C# SDK to populate `sdks/csharp/packages/**`. Then overlays Unity `.meta` skeleton files from `sdks/csharp/unity-meta-skeleton~/**` onto the restored versioned package directory, so Unity can associate stable meta files with the most recently built package.
+
+**Usage:**
+```bash
+Usage: dlls
+```
+
+**Options:**
+
+- `--help`: Print help (see a summary with '-h')
+
 ### `smoketests`
 
 Runs smoketests