refactor: change the native type for account IDs to reduce allocations

> One general comment: we frequently use `account.to_bytes()` to convert account ID to a vector of bytes. This results in allocations and I wonder if it would be better to use something like `u128` or `[u8; 15]` as a "native" type for account ID.

_Originally posted by @bobbinth in https://github.com/0xPolygonMiden/miden-node/pull/591#discussion_r1897462700_