Switch interpreter to use new base value types

The commit changes the interpreter and related code to use the new
`BaeValue` and `Number` types, moving away from direct floats. The main
changes include:

- Replace LiteralValue with BaeValue across the codebase - Add Number
enum for type-safe numeric values - Move AST definitions to common
module - Update operators to handle new numeric types - Add 'is' token
type and parser support Switch to common base_value library for value
types

This commit represents a significant refactoring to switch the
interpreter to use a new shared base value type system. The main changes
include:

1. Move value types to a new common/base_value.rs module 2. Add richer
numeric type support with promotion rules 3. Update interpreter to use
new BaseValue enum 4. Move AST types to common module for sharing 5.
Consolidate value operations like Add, Sub etc 6. Add proper test
coverage for numeric operations

The commit improves type safety and adds more robust numeric handling
while keeping the interpreter's core logic clean.

src/backend/environment.rs

@@ -1,13 +1,16 @@
 use std::collections::HashMap;
 
 use crate::{
-    frontend::{source_registry::SourceSlice, tokens::LiteralValue},
-    result::{runtime_error, LoxResult},
+    common::{
+        base_value::BaseValue,
+        lox_result::{runtime_error, LoxResult},
+    },
+    frontend::source_registry::SourceSlice,
 };
 
 #[derive(Debug, Clone, PartialEq)]
 pub struct EnvironmentStack {
-    stack: Vec<HashMap<String, LiteralValue>>,
+    stack: Vec<HashMap<String, BaseValue>>,
 }
 
 impl EnvironmentStack {
@@ -25,7 +28,7 @@ impl EnvironmentStack {
         self.stack.pop();
     }
 
-    pub fn get(&self, name: &str) -> LoxResult<LiteralValue> {
+    pub fn get(&self, name: &str) -> LoxResult<BaseValue> {
         let size = self.stack.len();
 
         for i in (0..size).rev() {
@@ -39,12 +42,12 @@ impl EnvironmentStack {
         )
     }
 
-    pub fn declare(&mut self, name: String, value: LiteralValue) -> LoxResult<LiteralValue> {
+    pub fn declare(&mut self, name: String, value: BaseValue) -> LoxResult<BaseValue> {
         self.stack.last_mut().unwrap().insert(name, value.clone());
         Ok(value)
     }
 
-    pub fn set(&mut self, name: String, value: LiteralValue) -> LoxResult<LiteralValue> {
+    pub fn set(&mut self, name: String, value: BaseValue) -> LoxResult<BaseValue> {
         let size = self.stack.len();
 
         for i in (0..size).rev() {