Implements public announcements encrypted via symmetric keys

This is most useful for utxos that transfer funds within a single
wallet such as change addresses.

compared to on-chain pub-key public announcements:

Data encrypted with symmetric keys is smaller than data encrypted with
asymmetric keys so there is a blockchain space (and thus fee) savings.

compared to off-chain expected utxos:

symmetric-key announcements exist on the blockchain and thus are
immune to local data-loss situations.  off-chain expected utxos do not
use any blockchain space but require that the wallet holder make
ongoing backups of wallet state and never lose them.

code:
 * simplified `UtxoNotifyMethod` to `OnChain`, `OffChain`
 * simplified `UtxoNotifcation` to `OnChain(_)`, `OffChain(_)`
 * removed `UtxoNotifyMethodSpecifier`
 * change logic in `TxOutput::auto()`
 * add `KeyType` enum to improve abstraction
 * refactor common key logic into address::common
 * simplify WalletState::scan_for_announced_utxos()
 * simplify WalletState::find_spending_key_for_utxo()
 * add WalletState::get_all_known_spending_keys()
 * new param `owned_utxo_output_method` for `generate_tx_outputs()`
 * new param `change_key` for `create_transaction()
 * new param `key_type` for `next_receiving_address()` rpc
 * neptune-cli generate-wallet: remove display of first wallet addr
   as it should not be considered special/only.

docs:
 * document keys and addresses in mdbook
 * document utxo notifications in mdbook
 * add/update type/method doc-comments
 * add some missing module doc-comments

tests:
 * consolidate all key/addr tests into address_type::test
 * same test logic applies to both symmetric and generation keys
 * make all key tests into proptests (symmetric and generation)
 * make transaction_output tests more comprehensive

SpendingKey          --> GenerationSpendingKey
ReceivingAddress     --> GenerationReceivingAddress
SpendingKeyType      --> SpendingKey
ReceivingAddressType --> ReceivingAddress

we don't need to call add_expected_utxos_to_wallet() if there are not
any offchain expected_utxos.

1. Adds a Debug impl that displays to_string() value.  Useful when
reading failed assertions about coin amounts.

2. Adds From<u8>, From<u16>, From<u32> infallible conversions.
Makes it easy to do things like 42u8.into()

Adds tests for restoring a wallet from seed and verifying if balance
is correct after performing both onchain and offchain notifications.

demonstrates that offchain notifications are very risky and can
lead to loss-of-funds even when wallet-owner has the seed backed up.

1. update a couple crates in Cargo.lock where the old version was
   failing with rustc 1.80

2. workaround rust stack overflow when compiling triton-vm

fixes some indentation warnings that are new in clippy 1.80