Give allocation control to the caller instead of force a clone (#2389)

Achieved by moving the boxes out of the temporary reference wrappers which are
cloneable themselves, i.e. if required the caller can clone them already or
consume them to reuse existing allocations.

src/schema/document/value.rs

@@ -27,7 +27,7 @@ pub trait Value<'a>: Send + Sync + Debug {
     }
 
     #[inline]
-    /// If the Value is a String, returns the associated str. Returns None otherwise.
+    /// If the Value is a leaf, returns the associated leaf. Returns None otherwise.
     fn as_leaf(&self) -> Option<ReferenceValueLeaf<'a>> {
         if let ReferenceValue::Leaf(val) = self.as_value() {
             Some(val)
@@ -82,7 +82,8 @@ pub trait Value<'a>: Send + Sync + Debug {
     /// If the Value is a pre-tokenized string, returns the associated string. Returns None
     /// otherwise.
     fn as_pre_tokenized_text(&self) -> Option<Box<PreTokenizedString>> {
-        self.as_leaf().and_then(|leaf| leaf.as_pre_tokenized_text())
+        self.as_leaf()
+            .and_then(|leaf| leaf.into_pre_tokenized_text())
     }
 
     #[inline]
@@ -259,11 +260,11 @@ impl<'a> ReferenceValueLeaf<'a> {
     }
 
     #[inline]
-    /// If the Value is a pre-tokenized string, returns the associated string. Returns None
-    /// otherwise.
-    pub fn as_pre_tokenized_text(&self) -> Option<Box<PreTokenizedString>> {
+    /// If the Value is a pre-tokenized string, consumes it and returns the string.
+    /// Returns None otherwise.
+    pub fn into_pre_tokenized_text(self) -> Option<Box<PreTokenizedString>> {
         if let Self::PreTokStr(val) = self {
-            Some(val.clone())
+            Some(val)
         } else {
             None
         }
@@ -322,6 +323,16 @@ where V: Value<'a>
         }
     }
 
+    #[inline]
+    /// If the Value is a leaf, consume it and return the leaf. Returns None otherwise.
+    pub fn into_leaf(self) -> Option<ReferenceValueLeaf<'a>> {
+        if let Self::Leaf(val) = self {
+            Some(val)
+        } else {
+            None
+        }
+    }
+
     #[inline]
     /// If the Value is a String, returns the associated str. Returns None otherwise.
     pub fn as_str(&self) -> Option<&'a str> {
@@ -365,10 +376,11 @@ where V: Value<'a>
     }
 
     #[inline]
-    /// If the Value is a pre-tokenized string, returns the associated string. Returns None
-    /// otherwise.
-    pub fn as_pre_tokenized_text(&self) -> Option<Box<PreTokenizedString>> {
-        self.as_leaf().and_then(|leaf| leaf.as_pre_tokenized_text())
+    /// If the Value is a pre-tokenized string, consumes it and returns the string.
+    /// Returns None otherwise.
+    pub fn into_pre_tokenized_text(self) -> Option<Box<PreTokenizedString>> {
+        self.into_leaf()
+            .and_then(|leaf| leaf.into_pre_tokenized_text())
     }
 
     #[inline]