no-std/alloc: fix a couple "unused import" warnings

Author: apoelstra

src/primitives/encode.rs

@@ -40,7 +40,6 @@
 //! }
 //! ```
 
-use core::iter::Iterator;
 use core::marker::PhantomData;
 
 use crate::primitives::checksum::HrpFe32Iter;

src/primitives/hrp.rs

@@ -9,7 +9,7 @@
 //!
 //! ref: [BIP-173](https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki#user-content-Bech32)
 
-#[cfg(feature = "alloc")]
+#[cfg(all(feature = "alloc", not(feature = "std"), not(test)))]
 use alloc::string::String;
 use core::cmp::Ordering;
 use core::fmt::{self, Write};

src/segwit.rs

@@ -44,18 +44,17 @@
 use alloc::{string::String, vec::Vec};
 use core::fmt;
 
+#[cfg(feature = "alloc")]
 use crate::error::write_err;
 use crate::primitives::decode::SegwitCodeLengthError;
 #[cfg(feature = "alloc")]
 use crate::primitives::decode::{SegwitHrpstring, SegwitHrpstringError};
 use crate::primitives::gf32::Fe32;
 use crate::primitives::hrp::Hrp;
 use crate::primitives::iter::{ByteIterExt, Fe32IterExt};
+use crate::primitives::segwit::MAX_STRING_LENGTH;
 #[cfg(feature = "alloc")]
-use crate::primitives::segwit;
-use crate::primitives::segwit::{
-    InvalidWitnessVersionError, WitnessLengthError, MAX_STRING_LENGTH,
-};
+use crate::primitives::segwit::{self, InvalidWitnessVersionError, WitnessLengthError};
 use crate::primitives::{Bech32, Bech32m};
 
 #[rustfmt::skip]                // Keep public re-exports separate.