Simplify or remove CodeBuilder after the package migration

#3146 kept `CodeBuilder` working with packages, but the module now has adapter traits that mostly forward to package based assembly.

Motivating PR comment:

- https://github.com/0xMiden/protocol/pull/3146#discussion_r3516297135

The main path is [`crates/miden-standards/src/code_builder/mod.rs`](https://github.com/0xMiden/protocol/blob/2432a082e53c7e16b2885c8ee42e05489480358c/crates/miden-standards/src/code_builder/mod.rs#L33-L120). The package migration version is on #3146, so this permalink points at the PR head.

Please decide whether `CodeBuilder` should stay as a public helper.

If it stays, make it smaller:

- accept package values directly where possible.
- avoid broad adapter traits unless a caller needs them.
- keep note script source parsing close to the one call site.

If it no longer earns its place, remove it and update tests to use the package assembly APIs directly.