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

[tomyrd]

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 #591 (comment)

[tomyrd]

With the changes in #603 the number of allocations is reduced greatly. Would this be enough or we still want to change the native type in the node? The miden-base type has its benefits as it has additional methods that could be useful.