feat(migrate): implement storage layout introspection and hazard analysis helpers

[ibrahimmujidah1-stack]

Summary

Implements automated storage layout introspection and migration hazard analysis for Soroban contracts:

• Introspection Engine (\src/utils/storage_layout.rs): Parses Rust contract definitions and specs to extract storage keys, storage tiers (\Instance, \Persistent, \Temporary), value types, and \DataKey\ enum variants with discriminants.
• Hazard Detection: Automatically detects breaking changes between contract versions (removed keys, type mutations, storage tier shifts, discriminant renumbering, and uninitialized keys).
• Automated Rule Generation: Generates starter migration rules files ready for dry-run testing.
• CLI Subcommands (\src/commands/migrate.rs):
  • \starforge migrate introspect \ (with --json\ output)
  • \starforge migrate hazards --old --new \ (with --json\ and --output-rules )
• Unit Tests: Full test coverage of layout extraction, breaking hazard detection, and safe layout verification.
• Documentation (\docs/STORAGE_LAYOUT_MIGRATIONS.md): Guide on introspecting layouts, resolving migration hazards, and running state migrations safely.

Closes #803

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