feat: support explicit Rust Box value inspection

[swananan]

Summary

• document explicit dereference as the safe way to inspect sized Rust
  Box<T> values because rustc emits them as ordinary pointer DWARF
• verify pointer-root and pointee adapter behavior across the supported rustc
  compatibility matrix
• add host e2e coverage for Box<i32>, Box<String>, and Box<Struct>
• explain why the Rust adapter must not classify ordinary pointers as boxes

Testing

• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test -p ghostscope-dwarf --all-features
• full supported rustc compatibility matrix
• focused sized Box host e2e, runner job 6519244c49f6
• full standard host e2e, runner job fbb7b081a9fe

Container topology e2e was intentionally skipped because this change does not
affect container, PID namespace, sandbox, or runner-topology behavior.