[Stage 3] Define provider adapter package boundaries

[Will-thom]

Goal: define where optional provider adapter code should live without coupling it to the core analyzer.

Related plan: #82.

Depends on: #79 and #22.

Acceptance criteria:
- Propose package boundaries for core analyzer, provider interfaces, and provider implementations.
- Explain what cannot import provider-specific code.
- Include testability expectations for adapters.
- Document how this preserves local-first behavior.

[github-actions]

Hi @Will-thom, thank you for contributing to PR Maven CLI.

I appreciate the time you spent opening this issue. This project is intentionally shaped for focused, reviewable open source contributions, so your input helps the tool become more useful for Java and Maven teams.

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