userland: search and exec tools, spawn library (T14)

rg (ripgrep 15.2), grep (ours, on ripgrep's regex crates), find and xargs
(ours), sed (uutils 0.3 wrapper), diff and cmp (uutils diffutils 0.6 with -r),
fd 10.5, jaq 2.3, env and timeout. userland/spawn is a small Command-like
client of the process interface. search-test.nu: 42 cases match native tools.

userland/diffutils/.github/workflows/wasi.yml

@@ -0,0 +1,28 @@
+# spell-checker:ignore wasip
+name: WASI
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: read
+
+# End the current execution if there is a new changeset in the PR.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
+
+jobs:
+  test_wasi:
+    name: Tests
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v7
+    - uses: dtolnay/rust-toolchain@stable
+      with:
+        targets: wasm32-wasip1
+    - name: check
+      run: cargo check --target wasm32-wasip1