Rebuild source dependencies when package output settings change

[cknitt]

Problem

Rewatch can reuse stale dependency build artifacts when projects with different package-specs build the same source dependency.

We encountered this while working on moving Belt into the separate @rescript/belt package in the ReScript compiler repository:

1. The regular analysis tests build @rescript/belt through a CommonJS test project.
2. The reanalyze tests subsequently use the same package through an ES module test project.
3. Both projects reference the same source dependency and therefore share its build artifacts.
4. Rewatch considers the existing Belt artifacts current and does not rebuild them for the second project.
5. The reanalyze tests fail with a misleading Missing dependency Belt_* error.

This is not a particularly common project setup, but the compiler repository exposes the underlying invalidation problem because multiple test projects with different output formats build the same source dependency in sequence.

Dependencies are compiled using the consuming root project's package output settings. However, these settings are not recorded in lib/bs/compiler-info.json. Belt's .cmj files therefore still contain only the CommonJS package-output metadata when the ES module project is built.

The dependency files and compiler search path are present; it is the package-output metadata inside the .cmj files that is stale.

Proposed solution

Include the effective root package output settings in each package's compiler-info.json.

The stored value should contain a normalized representation of every effective package spec, including:

• Module format
• in-source
• Resolved suffix, including the root-level suffix fallback

During initialization, compare the current package output settings with those stored in compiler-info.json. If they differ, clean and rebuild the affected dependency.

This follows the existing mechanism that invalidates dependency builds when root source-map arguments change.

Testing

Add an integration test with two projects sharing a source dependency:

1. Build the dependency through a CommonJS project.
2. Build it through an ES module project without explicitly cleaning the dependency.
3. Verify that Rewatch rebuilds the dependency and that the second project compiles successfully.

Ideally, test the reverse order as well.