Simpler decorators removal from `ProvenTransaction` and `ProvenBatch`

In https://github.com/0xMiden/miden-node/pull/1194 the decorators removal in received `ProvenTransaction` and `ProvenBatch` was added, but due to the lack of accessors and mutators to the `MAST` of the note script we needed to dismember the original structs to then change the `MAST` and rebuild the, now without decorators` struct.

We need to investigate for a way to remove decorators easier from the mentioend structs, without having to clone so much and less error-prone.