ci: measure and report CLI load time, and require subsecond

Also, revert this commit:
 2023-09-13 acd724e Eric Joanis ci: suppress redundant tests runs on PR and push
It turns out doing CI on review_requested is not great, because:
 - if you request 2 or 3 reviews, it triggers the action 2 or 3 times
 - when the branch needs a real merge, we do want the result of the merge
   tested in CI, so we lost important validation

.github/workflows/tests.yml

@@ -1,8 +1,7 @@
 name: Run Tests
 on:
-  pull_request:
-    types: [review_requested]
-  push:
+  - pull_request
+  - push
 
 jobs:
   test:
@@ -53,6 +52,32 @@ jobs:
           token: ${{ secrets.CODECOV_TOKEN }}  # optional but apparently makes upload more reliable
           fail_ci_if_error: false # too many upload errors to keep "true"
 
+      - name: Make sure the CLI stays fast
+        id: cli-load-time
+        run: |
+          PYTHONPROFILEIMPORTTIME=1 readalongs -h 2> importtime.txt > /dev/null
+          CLI_LOAD_TIME="$((/usr/bin/time --format=%E readalongs -h > /dev/null) 2>&1)"
+          echo "CLI load time: $CLI_LOAD_TIME"
+          echo "CLI load time: $CLI_LOAD_TIME" > import-message.txt
+          echo "PR head ${{ github.event.pull_request.head.sha }}" >> import-message.txt
+          echo "Imports that take more than 0.1 s:" >> import-message.txt
+          grep -E 'cumulative|[0-9]{6} ' importtime.txt >> import-message.txt
+          cat import-message.txt
+          echo "Full import time log:"
+          cat importtime.txt
+          if [[ "$CLI_LOAD_TIME" > "0:01.00" ]]; then \
+            echo "ERROR: readalongs --help is too slow."; \
+            echo "Please run 'PYTHONPROFILEIMPORTTIME=1 readalongs -h 2> importtime.txt; tuna importtime.txt' and tuck away expensive imports so that the CLI doesn't load them until it uses them."; \
+            false; \
+          fi
+
+      - name: Report help speed in a PR comment
+        if: github.event_name == 'pull_request'
+        uses: mshick/add-pr-comment@v2
+        with:
+          preformatted: true
+          message-path: import-message.txt
+
   test-on-windows:
     runs-on: windows-latest
     if: ${{ !contains(github.event.head_commit.message, '#no-ci') }}