chore: restructure tests (#7793)

Follow up to https://github.com/ChainSafe/lodestar/pull/7610 with a few
restructuring suggestions, see comments below for detailed changes,
revives constants tests we are no longer running in CI and makes each
package executable separately again, ie. `cd packages/<package-name>`
into `yarn test:unit` works for all packages again.

One major change is that unit tests default should be written with
`mainnet` preset in mind as I noticed that makes a lot more sense for a
bunch of existing tests, eg. we have tests that depend on external
fixtures, like api spec tests for events and those are not compatible
with `minimal` preset. Also there doesn't seem to be much downside in
most cases for unit tests to use `mainnet` preset as it does not run
through all the epoch, like for example a e2e or sim test does. So
overall, it allows us to use mainnet fixtures / more "real world" data
which seems better with little to no downside.


Time comparison running unit tests on `unstable` vs. this branch

**unstable**

![image](https://github.com/user-attachments/assets/ba9c8e68-ec1a-4cb7-90fc-eb00cedae4bf)

**nflaig/restructure-tests**

![image](https://github.com/user-attachments/assets/0ffab5a4-4a71-42e1-a26e-32fc5627b873)

There is just a difference of 2 seconds (might be a fluke) in a 6 minute
run, this seems acceptable to me considering the benefits of using
`mainnet` preset noted above.

vitest.config.ts

@@ -1,17 +1,17 @@
 import path from "node:path";
 import {defineConfig} from "vitest/config";
 import {browserTestProject} from "./configs/vitest.config.browser.js";
-import {e2eMainnetProject, e2eProject} from "./configs/vitest.config.e2e.js";
+import {e2eMainnetProject, e2eMinimalProject} from "./configs/vitest.config.e2e.js";
 import {specProjectMainnet, specProjectMinimal} from "./configs/vitest.config.spec.js";
 import {typesTestProject} from "./configs/vitest.config.types.js";
-import {unitTestMainnetProject, unitTestProject} from "./configs/vitest.config.unit.js";
+import {unitTestMainnetProject, unitTestMinimalProject} from "./configs/vitest.config.unit.js";
 
 export default defineConfig({
   test: {
     workspace: [
       {
         extends: true,
-        ...unitTestProject,
+        ...unitTestMinimalProject,
       },
       {
         extends: true,
@@ -23,7 +23,7 @@ export default defineConfig({
       },
       {
         extends: true,
-        ...e2eProject,
+        ...e2eMinimalProject,
       },
       {
         extends: true,