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/codspeed.yml

@@ -0,0 +1,37 @@
+name: CodSpeed
+
+on:
+  push:
+    branches:
+      - "main"
+  pull_request:
+  # `workflow_dispatch` allows CodSpeed to trigger backtest
+  # performance analysis in order to generate initial data.
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  id-token: write
+
+jobs:
+  codspeed:
+    name: Run benchmarks
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+
+      - name: Setup rust toolchain, cache and cargo-codspeed binary
+        uses: moonrepo/setup-rust@v1
+        with:
+          channel: stable
+          cache-target: release
+          bins: cargo-codspeed
+
+      - name: Build the benchmark target(s)
+        run: cargo codspeed build -m simulation
+
+      - name: Run the benchmarks
+        uses: CodSpeedHQ/action@v5
+        with:
+          mode: simulation
+          run: cargo codspeed run