feat(bench): add safety number & epoch rotation benchmarks, CI workflow

Add safety_number benchmark to crypto_benchmarks.rs, epoch rotation
(propose_self_update + commit) benchmark to mls_operations.rs, expand
add_member group sizes to include 100, and add .github/workflows/bench.yml
that runs Criterion benchmarks and uploads HTML reports as artifacts.

.github/workflows/bench.yml

@@ -0,0 +1,54 @@
+name: Benchmarks
+
+on:
+  push:
+    branches: [main, v2]
+  pull_request:
+    branches: [main, v2]
+  workflow_dispatch:
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  bench:
+    name: Run Criterion benchmarks
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust
+        uses: dtolnay/rust-action@stable
+
+      - name: Install capnp
+        run: sudo apt-get update && sudo apt-get install -y capnproto
+
+      - name: Cache cargo
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ runner.os }}-bench-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-bench-
+
+      - name: Run benchmarks
+        run: cargo bench --package quicproquo-core -- --output-format=bencher 2>&1 | tee bench-output.txt
+
+      - name: Upload HTML reports
+        uses: actions/upload-artifact@v4
+        if: always()
+        with:
+          name: criterion-reports
+          path: target/criterion/
+          retention-days: 30
+
+      - name: Upload raw output
+        uses: actions/upload-artifact@v4
+        if: always()
+        with:
+          name: bench-output
+          path: bench-output.txt
+          retention-days: 30