Allow user to define partition column schema

- Allow user to define partition column schema
- Refactor unit tests

rust/src/schema/mod.rs

@@ -3,8 +3,9 @@
 
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
-use std::borrow::Cow;
+use std::borrow::{Borrow, Cow};
 use std::collections::HashMap;
+use std::hash::{Hash, Hasher};
 
 use crate::errors::DeltaTableError;
 
@@ -165,6 +166,20 @@ pub struct SchemaField {
     metadata: HashMap<String, Value>,
 }
 
+impl Hash for SchemaField {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.name.hash(state);
+    }
+}
+
+impl Borrow<str> for SchemaField {
+    fn borrow(&self) -> &str {
+        self.name.as_ref()
+    }
+}
+
+impl Eq for SchemaField {}
+
 impl SchemaField {
     /// Create a new SchemaField from scratch
     pub fn new(