Migrate tests to the spec-node runner

[fsoikin]

Description of the change

So here it is, as promised, the shiny new spec runner that persists results and takes command-line options.

Full docs here: https://purescript-spec.github.io/purescript-spec/running/#running-under-node

But here are some examples of possible use:

 λ npx spago test -- -E "ModuleParser|bundle"

Running tests for package: docs-search-index
ModuleParser
  ✓︎ test #0
  ✓︎ test #1
  ✓︎ test #2
  ✓︎ test #3
  ✓︎ test #4
  ✓︎ test #5
  ✓︎ test #6
  ✓︎ test #7
  ✓︎ multiline comment #1
  ✓︎ multiline comment #1
  ✓︎ multiline comment #1
  ✓︎ single line comment #1
  ✓︎ single line comment #1
Modules in .spago: 1113
  ✓︎ Parses every module in .spago/

Summary
14/14 tests passed


✓ Test succeeded for package "docs-search-index".

Running tests for package: spago
spago » bundle
  ✓︎ bundles into an app (browser)
  ✓︎ bundles into an app (node)
  ✓︎ bundles into a module
  ✓︎ bundles an app with source map (browser)
  ✓︎ bundles an app with source map (node)
  ✓︎ bundles a module with source map
  ✓︎ bundles a module with extra esbuild arguments
  ✓︎ refuses to overwrite existing bundle that is not Spago-generated
  ✓︎ overwrites non-Spago-generated bundle when there is no magic marker file

Summary
9/9 tests passed


✓ Test succeeded for package "spago".

 λ npx spago test -- -e "into an app (browser)" --timeout 1

Running tests for package: docs-search-index

Summary
0/0 tests passed


✓ Test succeeded for package "docs-search-index".

Running tests for package: spago
spago » bundle
  ✗ bundles into an app (browser):

  test timed out after 1000ms

Summary
0/1 test passed


✘ Tests failed for package "spago".

 λ npx spago test -- --only-failures

Running tests for package: docs-search-index

Summary
0/0 tests passed


✓ Test succeeded for package "docs-search-index".

Running tests for package: spago
spago » bundle
  ✓︎ bundles into an app (browser)

Summary
1/1 test passed


✓ Test succeeded for package "spago".

Checklist:

• Added the change to the "Unreleased" section of the changelog
• [ ] Added some example of the new feature to the README
• [ ] Added a test for the contribution (if applicable)

[f-f]

This is amazing, thank you!

We should add some docs for this:

• for the contributors (in the CONTRIBUTING.md), I think the --example and --example-matches are the most useful flags to know about
• and for users, since the question "can I select a subset of tests" comes up often. This section could be expanded to note that you can pass flags to the running tests and select things with --example if using the spec-node runner

[fsoikin]

Added docs. Let me know if it's acceptable.

[f-f]

This is great 👏