dev: add fast-unit test scripts excluding example tests

[Dotims]

What

Adds test:fast-unit and test:fast-unit-watch to the root package.json.
They run the unit tests but exclude the example tests in
apps/typegpu-docs/tests/individual-example-tests, for a faster local loop.

Closes #1638

Note on the approach

The issue suggests handling this like the browser tests (by project). On
Vitest 4, though, the inner individual-example-tests project defined in
apps/typegpu-docs/vitest.config.mts is not addressable from the monorepo
root: when that config is pulled in via the root projects: ['apps/*'], its
nested test.projects is not re-expanded, so the example tests run under the
typegpu-docs project and --project=!individual-example-tests is a no-op.

I excluded them by path instead: --exclude '**/individual-example-tests/**'.
apps/typegpu-docs has no other node tests, so nothing else is affected.

Result: test:fast-unit runs 2508 tests across 192 files (vs 2567 / 251 with
the examples) and is noticeably faster.

Happy to instead restructure the config so the example tests become a
root-addressable project (then --project=!individual-example-tests) if you
prefer that.

Side note (out of scope for this PR)

--project=!browser in the existing scripts also looks like a no-op from the
root, and test:browser (--project browser) errors with "No projects
matched" when run from the root. Possibly fallout from the Vitest 3->4 upgrade.

[Copilot]

Pull request overview

Adds new root-level Vitest scripts intended to speed up local unit-test runs by excluding the apps/typegpu-docs/tests/individual-example-tests suite, addressing issue #1638.

Changes:

• Add test:fast-unit to run unit tests while excluding **/individual-example-tests/**.
• Add test:fast-unit-watch to run the same filtered set in watch mode.

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[pullfrog]

ℹ️ No critical issues — minor suggestions inline.

Reviewed changes — adds test:fast-unit and test:fast-unit-watch scripts to the root package.json that skip the example snapshot tests in apps/typegpu-docs/tests/individual-example-tests, giving a faster local unit-test loop.

• Add test:fast-unit — runs the non-browser unit tests while excluding the example tests.
• Add test:fast-unit-watch — watch-mode equivalent of the above.

  ^{｜ Fix all ➔ ｜ Fix 👍s ➔ ｜ View workflow run ｜ Using Kimi K2 (free via Pullfrog for OSS) ｜ 𝕏}

[iwoplaza]

Thanks a lot! 💜