carrot+fcmp: misc refactors of tx_builder b4 hot/cold support

* info fetchers for `tx_reconstruct_variant_t`
* expose `collect_non_burned_transfers_by_onetime_address()`
* add `collect_selected_transfer_indices()`
* document and cleanup `sign_carrot_transaction_proposal()`
* finalize proofs in `finalize_all_proofs_from_transfer_details()` with transfer details
* `make_pending_carrot_tx()` without transfers list or `hw::device` needed

Author: jeffro256