ci Don't always re-install dependencies, which speeds up successive b…

…uilds

(Sample size: 1)

Now (some output ommitted):

    # Do a clean build
    rm -rf .tox; time tox
    tox  17.25s user 8.84s system 49% cpu 52.303 total
    # Do a successive build
    time tox
    tox  1.72s user 0.38s system 86% cpu 2.436 total

Before (some output ommitted):

    # Do a clean build
    rm -rf .tox; time tox
    tox  19.69s user 11.41s system 46% cpu 1:06.32 total
    # Do a successive build
    time tox
    tox  3.57s user 3.64s system 24% cpu 29.537 total

It can go _faster_, but that'd come at the cost of having tox managing our
dependencies when they change, so I opted not to do that. Though, we should
keep that in our back pocket if we get to that point.

ci/node-install.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+set -eu
+
+if [ -f "$TOX_ENV_DIR/bin/node" ]; then
+    echo Node and friends already installed.
+    exit 0
+fi
+
+nodeenv --prebuilt -p --node 18.20.4 "$TOX_ENV_DIR"
+npm install -g npm@latest
+npm ci

tox.ini

@@ -1,19 +1,31 @@
 [tox]
 env_list =
-    node, eslint, stylelint, pylint, py312
+    pytest
+    pylint
+    eslint
+    stylelint
 minversion = 4.6.0
 skip_missing_interpreters = false
 
 [testenv]
-description = run the tests with pytest
+description = base environment
 package = wheel
 wheel_build_env = .pkg
 deps =
+    pytest: -r requirements.txt
+    eslint,stylelint: nodeenv
+commands_pre =
+    {es,style}lint: ./ci/node-install.sh
+allowlist_externals =
+    {es,style}lint: ./ci/node-install.sh
+
+[testenv:pytest]
+description = run the tests with pytest
+deps =
+    {[testenv]deps}
     pytest>=6
     pytest-mock>=3
-    -rrequirements.txt
-commands =
-    pytest {tty:--color=yes} {posargs}
+commands = pytest {tty:--color=yes} {posargs}
 
 [testenv:pylint]
 description = run python black linters
@@ -22,39 +34,12 @@ deps =
     black==24.8.0
 commands = black --check {posargs: ./tests ./dashboard}
 
-[testenv:node]
-description = setup Node.js environment
-skip_install = true
-deps =
-    nodeenv
-commands =
-    nodeenv --prebuilt -p --node 18.20.4
-    npm install -g npm@latest
-allowlist_externals =
-    node
-    npm
-    npx
-
 [testenv:eslint]
 description = run eslint
 skip_install = true
-deps =
-    {[testenv:node]deps}
-commands =
-    {[testenv:node]commands}
-    npm ci
-    npm run lint:js
-depends = node
-allowlist_externals = npm
+commands = npm run lint:js
 
 [testenv:stylelint]
 description = run stylelint
 skip_install = true
-deps =
-    {[testenv:node]deps}
-commands =
-    {[testenv:node]commands}
-    npm ci
-    npm run lint:css
-depends = node
-allowlist_externals = npm
+commands = npm run lint:css