[test] Rewrites sigma.js testing

Details:
- Moves everything testing related to the new test package
- Rewrites unit testing to be based on Vitest, with its browser mode, so
  that it works in an actual environment
- Rewrites e2e testing to be based on Playwright, so that there is less
  code and it is more maintainable
- Rewrites benchmarking to be based on Vitest and its benchmark mode (it
  does not work yet though)

Also, some various random changes blend into this huge refactoring:
- Fixes tiny dependency issues here and there
- Renames vite.config.ts as vite.config.mts to clear some annoying
  warnings
- Fixes root build task, to include sigma bundle generation

.gitignore

@@ -11,9 +11,9 @@ node_modules
 build
 dist
 /www
-packages/sigma/test/e2e/reports
-packages/sigma/test/e2e/screenshots/*.current.png
-packages/sigma/test/e2e/screenshots/*.diff.png
+packages/test/e2e/reports
+packages/test/e2e/screenshots/*.current.png
+packages/test/e2e/screenshots/*.diff.png
 packages/storybook/storybook-static
 
 # Built sources:

README.md

@@ -55,38 +55,6 @@ _List of available examples_
 
 Also, a more realistic sigma.js based web application is available in the [`demo`](https://github.com/jacomyal/sigma.js/tree/main/packages/demo) folder. It aims to show a real-world usecase, and is the main showcase of [sigma.js website](https://www.sigmajs.org/).
 
-## Testing
-
-Some minor helpers are unit tested, but the main way sigma.js is tested is with generated screenshots. Those screenshots are generated with [Puppeteer](https://pptr.dev/) on a headless Chrome/Chromium. Also, there are now some benchmarking scenarii, to ensure some features do not bring a bad impact on performances.
-
-You can check that everything is fine (unit tests and screenshots) by simply running:
-
-```bash
-npm run test
-```
-
-If at some point, you actually have a good reason to break some screenshots, you can run `npm run e2e:generate-screenshots` to erase reference screenshots.
-
-## Benchmarking
-
-You can run the benchmark scenarii by running:
-
-```bash
-cd path/to/sigma.js
-cd packages/sigma
-npm run e2e:benchmark -- --filename my-report.json
-```
-
-This will generate a JSON report at `test/e2e/reports/my-report.json`.
-
-Then, you can compare it to some reference report, by running:
-
-```bash
-cd path/to/sigma.js
-cd packages/sigma
-npm run e2e:compare-benchmarks -- --reference test/e2e/reports/reference-report.json --report test/e2e/reports/my-report.json
-```
-
 ## Website
 
 The current website is based on [Docusaurus](https://docusaurus.io/), with a static homepage. It is located in the `website` folder. It also showcases the React.js based demo available in the [`demo`](https://github.com/jacomyal/sigma.js/tree/main/packages/demo) folder in an iframe. The website itself does not need any build step, though the demo does.