test(client-local-server-*tests): test ESM

[jason-ha]

Stop "lying" that ESM is tested (there was not CJS test label) and actually test ESM that we care more about. Note that all server packages (server workspaces) are CJS only.

1. Update packages to type "module" (ESM)
   • ran ts2esm that added missing .js extensions to import spec
   • dirname.cts removed in favor of ESM only import.meta.url use.
2. Adopt standardized test patterns
   • Move files spec from mocha command lines (was ignored) to config file.
   • Move test support files under src/test instead of just src/.
   • Move stress package tsconfig.json to under src/test.
3. Fix sequence build deps to allow build-and-test:unit:esm from stress package.

[github-actions]

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[Copilot]

Pull request overview

This PR converts local server test packages toward ESM-based test execution and reorganizes local-server stress test support code under src/test, while updating build/test scripts and dependencies to target ESM outputs.

Changes:

• Switch local-server test packages from CommonJS to ESM test builds and Mocha config-based test discovery.
• Move/update stress harness utilities and imports to ESM-compatible paths.
• Split Sequence test build dependencies by CJS/ESM so ESM stress tests can depend on ESM test outputs.

Reviewed changes

Copilot reviewed 20 out of 27 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/test/local-server-tests/src/test/utils.ts	Adds local test loader helper under src/test.
packages/test/local-server-tests/src/test/tsconfig.json	Updates test compile root/output to lib/test.
packages/test/local-server-tests/src/test/synchronousDataStoreCreation.spec.ts	Updates helper import path.
packages/test/local-server-tests/src/test/stagingMode.spec.ts	Updates helper import path.
packages/test/local-server-tests/src/test/readonly.spec.ts	Updates helper import path.
packages/test/local-server-tests/src/test/pendingLocalStateStore.spec.ts	Updates helper import path.
packages/test/local-server-tests/src/test/loadFrozenContainerFromPendingState.spec.ts	Updates helper import path.
packages/test/local-server-tests/src/test/handleResolution.spec.ts	Updates helper import path and extension.
packages/test/local-server-tests/src/test/decoupledCreate.spec.ts	Updates helper import path.
packages/test/local-server-tests/src/test/captureFullContainerState.spec.ts	Updates helper import path.
packages/test/local-server-tests/package.json	Switches package/test scripts and fluid-build task to ESM.
packages/test/local-server-tests/.mocharc.cjs	Moves Mocha spec glob into config.
packages/test/local-server-stress-tests/src/test/utils.ts	Adds unreachable-code-path proxy helper.
packages/test/local-server-stress-tests/src/test/tsconfig.json	Moves stress test tsconfig under src/test and updates output.
packages/test/local-server-stress-tests/src/test/stressDataObject.ts	Adds stress test data object/runtime factory implementation.
packages/test/local-server-stress-tests/src/test/localServerStressHarness.ts	Adds local-server stress harness implementation.
packages/test/local-server-stress-tests/src/test/localServerStress.spec.ts	Updates stress test imports to local ESM paths.
packages/test/local-server-stress-tests/src/test/dynamicWeightGenerator.ts	Adds dynamic-weight async generator utility.
packages/test/local-server-stress-tests/src/test/ddsOperations.ts	Adds DDS operation conversion/reduction/validation helpers.
packages/test/local-server-stress-tests/src/test/ddsModels.ts	Adds DDS model registry for stress tests.
packages/test/local-server-stress-tests/src/test/dataStoreOperations.ts	Updates stress harness type import path.
packages/test/local-server-stress-tests/src/test/baseModel.ts	Updates imports and replaces CJS dirname helper with import.meta.url.
packages/test/local-server-stress-tests/src/dirname.cts	Removes CJS dirname shim.
packages/test/local-server-stress-tests/package.json	Switches package/test scripts and stress build dependencies to ESM.
packages/test/local-server-stress-tests/eslint.config.mts	Points ESLint parser at moved stress test tsconfig.
packages/test/local-server-stress-tests/.mocharc.cjs	Moves Mocha spec glob into config and preserves forced exit.
packages/dds/sequence/package.json	Splits merge-tree test build dependencies into CJS and ESM tasks.

[alexvy86]

Move files spec from mocha command lines (was ignored) [...]

Curious, why was it ignored?

[jason-ha]

Move files spec from mocha command lines (was ignored) [...]

Curious, why was it ignored?

Yes. As of #25292 most mocha command line test specifications are ignored.

[MarioJGMsoft]

I thought that mocha was only compatible with CJS? Why does this work here?