Fix chunk hash logic in hot-reloader for server components

[shuding]

Previously we were assuming that serverOnlyChanges is the same as "server component changes". However that's not always true, as one can change a component from server component to client component, or vice versa, where the change affects both server and client builds, so serverOnlyChanges will be empty.

This PR fixes the logic by strictly hashing and comparing modules in the server layer. Note that I intentionally skipped the test as this fix isn't complete.

NEX-30

Bug

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[timneutkens]

Looks good!