feat: restore TableRef::table_id (#1001)

This is a simple method that was accidentally removed. Now let's add it
back.

Author: iajoiner

crates/proof-of-sql/src/base/database/table_ref.rs

@@ -48,8 +48,7 @@ impl TableRef {
         }
     }
 
-    /// Returns the identifier of the schema
-    /// # Panics
+    /// Returns the identifier of the schema if it exists. Otherwise returns `None`.
     #[must_use]
     pub fn schema_id(&self) -> Option<&Ident> {
         match self {
@@ -58,6 +57,17 @@ impl TableRef {
         }
     }
 
+    /// Returns the identifier of the table if it exists. Otherwise returns `None`.
+    #[must_use]
+    pub fn table_id(&self) -> Option<&Ident> {
+        match self {
+            Self::FullyQualified { table_name, .. } | Self::TableOnly { table_name } => {
+                Some(table_name)
+            }
+            Self::None => None,
+        }
+    }
+
     /// Creates a new table reference from an optional schema and table name.
     #[must_use]
     pub fn from_names(schema_name: Option<&str>, table_name: &str) -> Self {