refactor(parser): Step 1 - Extract common utilities module

Successfully extracted utility methods from parser/mod.rs to common.rs:
- Created ParserUtils trait with token manipulation methods
- Extracted current_token, peek_token, advance, skip_newlines, etc.
- All parser modules now use trait-based utilities
- Reduced mod.rs by ~60 lines

✅ Build successful with no errors
✅ All functionality preserved - tested with using nyashstd

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/parser/statements.rs

@@ -8,6 +8,7 @@
 use crate::tokenizer::TokenType;
 use crate::ast::{ASTNode, CatchClause, Span};
 use super::{NyashParser, ParseError};
+use super::common::ParserUtils;
 
 impl NyashParser {
     /// 文をパース