refactor: 寄存器号 u8→u32 全链放宽，vreg 化去 checkpoint/reg_overflow

crates/oxide_emit/src/stmt/block.rs

@@ -4,7 +4,7 @@ use crate::{CompileCtx, Emitter};
 use oxide_parser::Statement;
 
 impl Emitter {
-    fn emit_block_statement(&self, stmt: &Statement, ctx: &mut CompileCtx) -> Result<Option<u8>, String> {
+    fn emit_block_statement(&self, stmt: &Statement, ctx: &mut CompileCtx) -> Result<Option<u32>, String> {
         let Statement::BlockStatement(block) = stmt else {
             return Ok(None);
         };
@@ -19,7 +19,7 @@ impl Emitter {
         Ok(r)
     }
 
-    pub(crate) fn emit_block_domain(&self, stmt: &Statement, ctx: &mut CompileCtx) -> Result<Option<u8>, String> {
+    pub(crate) fn emit_block_domain(&self, stmt: &Statement, ctx: &mut CompileCtx) -> Result<Option<u32>, String> {
         match stmt {
             Statement::BlockStatement(_) => self.emit_block_statement(stmt, ctx),
             _ => Ok(None),