Add managed string and array reads

[ero-qt]

Depends on #146.
Part of #149.

Adds read_string and read_array to both backends' Module. The crate had no way to read a System.String or a managed array; the raw route is a fixed-size read at a memorized header offset, unchecked against the count and wrong at the other width.

• read_string reads the character count, then exactly that many UTF-16 characters. Counts past the buffer, negative counts, and null references fail rather than truncate.
• read_array does the same with the length, judged at pointer width before narrowing so a huge value can't slip through as its low half. Element type is the caller's claim, like Process::read; the docs list the mappings (managed char is u16, Rust char never matches).
• Both take the address the reference is stored at (a pointer path's end, a static table slot) and dereference at the module's own width, so 32-bit games need no special handling.

ArrayVec shows up in a public signature for the first time; the crate already re-exports arrayvec.