refactor(terraform): return a struct from module resolvers

[nikpivkin]

Description

ModuleResolver returned five values: fs.FS, source prefix, module directory, an applies flag and an error. The first three are one result that always travels together, and applies duplicated the error — resolveModule did not read it when err != nil.

Resolvers now return (resolvers.Result, error). An unhandled source is reported as resolvers.ErrNotApplicable; the chain skips it and propagates any other error.

The interface and the chain move from parser to resolvers, which they already depended on entirely. The entry point is resolvers.Resolve.

This also fixes a case in registryResolver: it ignored applies from its nested Remote.Resolve call, so a location Remote does not handle, for example an http:// URL, produced a nil fs.FS with no error, and the parser then failed on it. The chain now reports that the module could not be resolved.

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).