Merge rust-bitcoin#5136: Remove option from current_chunk function signature

fcfaafc Update API text files (Tobin C. Harding)
48352fe Remove option from current_chunk function signature (Tobin C. Harding)
d8dd960 consensus_encoding: Add a test for empty encoders (Tobin C. Harding)

Pull request description:

  The `Option` was observed to be pointless, we can just return the empty list.
      
  Note that the diff is noisy AF but there is basically no changes to the test logic which confirms the observation.
      
  (Andrew made the observation, Tobin needed tests to convince himself.)
  
  Note patch 1 adds an impl of `Encodable` for `&Script` - I can't remember what is the correct thing to do, we went through this before ...


ACKs for top commit:
  jrakibi:
    ACK rust-bitcoin@fcfaafc
  apoelstra:
    ACK fcfaafc; successfully ran local tests


Tree-SHA512: ac9632b978544b7280219274fc2953ed24d13c57e3ec7630ff9297781e8f2cbec9ae61862946c303047344bd22719df8e735a8578b85df2c1989f101e8bae8a9

Author: apoelstra

api/units/all-features.txt

@@ -1904,7 +1904,7 @@ pub fn bitcoin_units::amount::AmountDecoder::new() -> Self
 pub fn bitcoin_units::amount::AmountDecoder::push_bytes(&mut self, bytes: &mut &[u8]) -> core::result::Result<bool, Self::Error>
 pub fn bitcoin_units::amount::AmountDecoder::read_limit(&self) -> usize
 pub fn bitcoin_units::amount::AmountEncoder::advance(&mut self) -> bool
-pub fn bitcoin_units::amount::AmountEncoder::current_chunk(&self) -> core::option::Option<&[u8]>
+pub fn bitcoin_units::amount::AmountEncoder::current_chunk(&self) -> &[u8]
 pub fn bitcoin_units::amount::Denomination::arbitrary(u: &mut arbitrary::unstructured::Unstructured<'a>) -> arbitrary::error::Result<Self>
 pub fn bitcoin_units::amount::Denomination::clone(&self) -> bitcoin_units::amount::Denomination
 pub fn bitcoin_units::amount::Denomination::eq(&self, other: &bitcoin_units::amount::Denomination) -> bool
@@ -2023,7 +2023,7 @@ pub fn bitcoin_units::block::BlockHeightDecoderError::fmt(&self, f: &mut core::f
 pub fn bitcoin_units::block::BlockHeightDecoderError::from(never: core::convert::Infallible) -> Self
 pub fn bitcoin_units::block::BlockHeightDecoderError::source(&self) -> core::option::Option<&(dyn core::error::Error + 'static)>
 pub fn bitcoin_units::block::BlockHeightEncoder::advance(&mut self) -> bool
-pub fn bitcoin_units::block::BlockHeightEncoder::current_chunk(&self) -> core::option::Option<&[u8]>
+pub fn bitcoin_units::block::BlockHeightEncoder::current_chunk(&self) -> &[u8]
 pub fn bitcoin_units::block::BlockHeightInterval::add(self, rhs: &bitcoin_units::block::BlockHeightInterval) -> Self::Output
 pub fn bitcoin_units::block::BlockHeightInterval::add(self, rhs: bitcoin_units::block::BlockHeightInterval) -> Self::Output
 pub fn bitcoin_units::block::BlockHeightInterval::add_assign(&mut self, rhs: &bitcoin_units::block::BlockHeightInterval)
@@ -2168,7 +2168,7 @@ pub fn bitcoin_units::locktime::absolute::LockTimeDecoder::new() -> Self
 pub fn bitcoin_units::locktime::absolute::LockTimeDecoder::push_bytes(&mut self, bytes: &mut &[u8]) -> core::result::Result<bool, Self::Error>
 pub fn bitcoin_units::locktime::absolute::LockTimeDecoder::read_limit(&self) -> usize
 pub fn bitcoin_units::locktime::absolute::LockTimeEncoder::advance(&mut self) -> bool
-pub fn bitcoin_units::locktime::absolute::LockTimeEncoder::current_chunk(&self) -> core::option::Option<&[u8]>
+pub fn bitcoin_units::locktime::absolute::LockTimeEncoder::current_chunk(&self) -> &[u8]
 pub fn bitcoin_units::locktime::absolute::MedianTimePast::arbitrary(u: &mut arbitrary::unstructured::Unstructured<'a>) -> arbitrary::error::Result<Self>
 pub fn bitcoin_units::locktime::absolute::MedianTimePast::clone(&self) -> bitcoin_units::locktime::absolute::MedianTimePast
 pub fn bitcoin_units::locktime::absolute::MedianTimePast::cmp(&self, other: &bitcoin_units::locktime::absolute::MedianTimePast) -> core::cmp::Ordering
@@ -2439,7 +2439,7 @@ pub fn bitcoin_units::sequence::SequenceDecoderError::fmt(&self, f: &mut core::f
 pub fn bitcoin_units::sequence::SequenceDecoderError::from(never: core::convert::Infallible) -> Self
 pub fn bitcoin_units::sequence::SequenceDecoderError::source(&self) -> core::option::Option<&(dyn core::error::Error + 'static)>
 pub fn bitcoin_units::sequence::SequenceEncoder::advance(&mut self) -> bool
-pub fn bitcoin_units::sequence::SequenceEncoder::current_chunk(&self) -> core::option::Option<&[u8]>
+pub fn bitcoin_units::sequence::SequenceEncoder::current_chunk(&self) -> &[u8]
 pub fn bitcoin_units::time::BlockTimeDecoder::default() -> Self
 pub fn bitcoin_units::time::BlockTimeDecoder::end(self) -> core::result::Result<Self::Output, Self::Error>
 pub fn bitcoin_units::time::BlockTimeDecoder::new() -> Self
@@ -2451,7 +2451,7 @@ pub fn bitcoin_units::time::BlockTimeDecoderError::fmt(&self, f: &mut core::fmt:
 pub fn bitcoin_units::time::BlockTimeDecoderError::from(never: core::convert::Infallible) -> Self
 pub fn bitcoin_units::time::BlockTimeDecoderError::source(&self) -> core::option::Option<&(dyn core::error::Error + 'static)>
 pub fn bitcoin_units::time::BlockTimeEncoder::advance(&mut self) -> bool
-pub fn bitcoin_units::time::BlockTimeEncoder::current_chunk(&self) -> core::option::Option<&[u8]>
+pub fn bitcoin_units::time::BlockTimeEncoder::current_chunk(&self) -> &[u8]
 pub fn core::num::error::ParseIntError::from(value: bitcoin_units::parse_int::ParseIntError) -> Self
 pub fn i64::mul(self, rhs: &bitcoin_units::SignedAmount) -> Self::Output
 pub fn i64::mul(self, rhs: &bitcoin_units::result::NumOpResult<bitcoin_units::SignedAmount>) -> Self::Output