Merge rust-bitcoin#3793: Update regex lookahead to match when there are no characters

23f75a0 Update regex lookahead to match when there are no characters (Shing Him Ng)

Pull request description:

  Was working on rust-bitcoin#3777 and noticed that `amount::Denomination` didn't show up when running `contrib/api.sh units types`. There are some structs/enums in `api/<crate>/all-features.txt` that dont have a `\(`, `;`, or ` ` after the struct/enum name, and the line just ends, so matching the end of line `$` should also be added.

  This allows the script to find the additional type from `units`:
  `#[non_exhaustive] pub enum bitcoin_units::amount::Denomination`

  Also tested this in `primitives`, and it returned:
  ```
  script::Script
  BlockChecked
  BlockUnchecked
  absolute::LockTime
  block::Checked
  block::Unchecked
  locktime::absolute::LockTime
  locktime::relative::LockTime
  opcodes::Class
  opcodes::ClassifyContext
  relative::LockTime
  BlockHash
  BlockHeader
  CompactTarget
  Sequence
  TapBranchTag
  TapLeafHash
  TapLeafTag
  TapNodeHash
  TapTweakHash
  TapTweakTag
  Transaction
  TxIn
  TxMerkleNode
  TxOut
  Txid
  Witness
  WitnessCommitment
  WitnessMerkleNode
  Wtxid
  block::BlockHash
  block::Header
  block::Version
  block::WitnessCommitment
  merkle_tree::TxMerkleNode
  merkle_tree::WitnessMerkleNode
  opcodes::Opcode
  pow::CompactTarget
  script::ScriptBuf
  script::ScriptHash
  script::WScriptHash
  sequence::Sequence
  taproot::TapBranchTag
  taproot::TapLeafHash
  taproot::TapLeafTag
  taproot::TapNodeHash
  taproot::TapTweakHash
  taproot::TapTweakTag
  transaction::OutPoint
  transaction::Transaction
  transaction::TxIn
  transaction::TxOut
  transaction::Txid
  transaction::Version
  transaction::Wtxid
  witness::Witness
  ```

  vs without this update (on `master`):
  ```
  script::Script
  BlockHash
  CompactTarget
  Sequence
  TapLeafHash
  TapNodeHash
  TapTweakHash
  TxMerkleNode
  Txid
  WitnessCommitment
  WitnessMerkleNode
  Wtxid
  block::BlockHash
  block::Version
  block::WitnessCommitment
  merkle_tree::TxMerkleNode
  merkle_tree::WitnessMerkleNode
  pow::CompactTarget
  script::ScriptBuf
  script::ScriptHash
  script::WScriptHash
  sequence::Sequence
  taproot::TapLeafHash
  taproot::TapNodeHash
  taproot::TapTweakHash
  transaction::Txid
  transaction::Version
  transaction::Wtxid
  ```

ACKs for top commit:
  tcharding:
    ACK 23f75a0
  storopoli:
    ACK 23f75a0
  apoelstra:
    ACK 23f75a0; successfully ran local tests

Tree-SHA512: ce6a43d017bb4bc6317853a4646ce4a8dcf5ce957bb2b9cc50bbd333c6854efd7527c25571c1b30736ae496305fedcf876022ad26c50bee232150d308cb62d08

Author: apoelstra

contrib/api.sh

@@ -99,12 +99,12 @@ main() {
 
 # Print all public structs and enums.
 structs_and_enums() {
-    grep -oP 'pub (struct|enum) \K[\w:]+(?=\(|;| )' "$file" | sed "s/^${crate_full_name}:://"
+    grep -oP 'pub (struct|enum) \K[\w:]+(?=\(|;| |$)' "$file" | sed "s/^${crate_full_name}:://"
 }
 
 # Print all public structs and enums excluding error types.
 structs_and_enums_no_err() {
-    grep -oP 'pub (struct|enum) \K[\w:]+(?=\(|;| )' "$file" | sed "s/^${crate_full_name}:://" | grep -v Error
+    grep -oP 'pub (struct|enum) \K[\w:]+(?=\(|;| |$)' "$file" | sed "s/^${crate_full_name}:://" | grep -v Error
 }
 
 # Print all public traits.