BIP360: Pay to Merkle Root (P2MR) (#1670)

Review comments and assistance by:
  Armin Sabouri <armins88@gmail.com>
  D++ <82842780+dplusplus1024@users.noreply.github.com>
  Jameson Lopp <jameson.lopp@gmail.com>
  jbride <jbride2001@yahoo.com>
  Joey Yandle <xoloki@gmail.com>
  Jon Atack <jon@atack.com>
  Jonas Nick <jonasd.nick@gmail.com>
  Kyle Crews <kylecrews@Kyles-Mac-Studio.local>
  Mark "Murch" Erhardt <murch@murch.one>
  notmike-5 <notmike-5@users.noreply.github.com>
  Vojtěch Strnad <43024885+vostrnad@users.noreply.github.com>

Co-authored-by: Ethan Heilman <ethan.r.heilman@gmail.com>
Co-authored-by: Isabel Foxen Duke <110147802+Isabelfoxenduke@users.noreply.github.com>

bip-0360/ref-impl/rust/src/error.rs

@@ -0,0 +1,16 @@
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum P2MRError {
+
+    #[error("P2TR requires witness version of 1")]
+    P2trRequiresWitnessVersion1,
+
+
+    #[error("P2MR requires a script tree with at least one leaf")]
+    MissingScriptTreeLeaf,
+    
+    // We can add more specific error variants here as needed
+    #[error("Invalid script tree structure: {0}")]
+    InvalidScriptTree(String),
+}