refactor: Delete legacy external-resolution PackageInfo state (#13526)
## Intent
**Deletion gate** for Phase 3: once every consumer reads resolution
knowledge, remove legacy resolution state from `PackageInfo`, deferred
closure installation, and fallback rehash helpers so readiness belongs
to repository construction.
**Stack:** layer 4 / 5. Base = layer 3 (global hash).
## Changes
- Delete
`PackageInfo::{unresolved_external_dependencies,transitive_dependencies,external_deps_hash}`
- Delete deferred closure workers / `ensure_transitive_closures`
- Delete `get_external_deps_hash` fallback rehash helper
- Mark Phase 3 complete in `ARCHITECTURE.md`
## Out of scope
Total `PackageInfo` deletion, script/version payload, declaration-path
polish (layer 5).
## Testing
- `cargo test -p turborepo-repository --lib test_lockfile_traversal`
- `cargo test -p turborepo-lib --lib prune`
- `cargo test -p turborepo-task-hash --lib`
- `cargo test -p turborepo-frameworks --lib`
- `cargo clippy -p turborepo-repository -p turborepo-lib -p
turborepo-task-hash -p turborepo-frameworks -p turborepo-boundaries -p
turborepo-hash --all-targets -- -D warnings`
Closes TURBO-5814.
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Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Anthony Shew <anthonyshew@users.noreply.github.com>