Bump Vitest to v4 (#19216)

This PR bumps Vitest from v2 to v4. As far as I know we don't use any
Vitest specific features in our tests, but had to upgrade the
`vitest.workspace.ts` file to a `vitest.config.ts` file instead.

The only features we use are the typical `describe`, `it`, `test`, and
`expect` functions.

The only other part we use is `vi.spyOn` and `vi.fn` but those didn't
change in API either.

The test shards were removed to prevent errors. Not all suites have
enough files / tests to be broken up into 3 parts so Vitest now errors
when that happens.

### Test plan

1. All tests should pass in CI.
2. All integration tests should pass in CI.

---------

Co-authored-by: Jordan Pittman <jordan@cryptica.me>

.github/workflows/integration-tests.yml

@@ -103,18 +103,8 @@ jobs:
           CARGO_PROFILE_RELEASE_LTO: 'off'
           CARGO_TARGET_X86_64_PC_WINDOWS_MSVC_LINKER: 'lld-link'
 
-      - name: Test ${{ matrix.integration }} 1/3
-        run: pnpm run test:integrations ./integrations/${{ matrix.integration }} --shard 1/3
-        env:
-          GITHUB_WORKSPACE: ${{ github.workspace }}
-
-      - name: Test ${{ matrix.integration }} 2/3
-        run: pnpm run test:integrations ./integrations/${{ matrix.integration }} --shard 2/3
-        env:
-          GITHUB_WORKSPACE: ${{ github.workspace }}
-
-      - name: Test ${{ matrix.integration }} 3/3
-        run: pnpm run test:integrations ./integrations/${{ matrix.integration }} --shard 3/3
+      - name: Test ${{ matrix.integration }}
+        run: pnpm run test:integrations ./integrations/${{ matrix.integration }}
         env:
           GITHUB_WORKSPACE: ${{ github.workspace }}