zcash_client_sqlite::wallet::common::{select_unspent_notes, select_spendable_notes_matching_value} are misdocumented

[daira]

/// Implementation details:
///
/// - Notes with individual value *below* the ``MARGINAL_FEE`` will be ignored

Actually notes with individual value less than or equal to MARGINAL_FEE will be ignored.

Also, the :min_value parameter to the stmt_select_notes query is set to MARGINAL_FEE but the relevant filter condition is rn.value > :min_value, so the parameter is misnamed: it is not the minimum value considered economic. It is the maximum value considered uneconomic. I suggest renaming it to :max_uneconomic_value.

This is all very much a nit because select_unspent_notes is pub(crate), select_spendable_notes_matching_value is private, and the implementation does what is intended. Nevertheless it was briefly confusing to me when trying to determine whether notes of value exactly MARGINAL_FEE are selectable (quite sensibly, they are not).