Find a better solution for `arrayPacked` flag

We need a way to pad array items to 32 bytes, but not encode the length of the array. Right now we do that using the `arrayPacked` flag, but there might be a better solution for this that does not require an extra flag.

Start by tracing the existing uses of the `arrayPacked` flag through the TypeScript ABI encoding and decoding paths. Determine how array items are padded to 32 bytes without encoding the array length, then compare the current flag-based behavior with a possible replacement. Done means the behavior is preserved without requiring the extra flag and the relevant encoding and decoding cases remain consistent.

Written by the indexing model from the issue text.