Optimize integration test performance

### Summary

This PR improves the performance of integration tests by implementing compiled binary caching and optimizing compiler flags. The overall test suite execution time has been reduced by approximately 17% (from ~11.5s to ~9.5s).

### Performance Improvements

| Metric | Before | After | Improvement |
|--------|--------|-------|-------------|
| Full test suite | ~11.5s | ~9.5s | ~17% faster |
| Integration tests only | ~10.5s | ~8.3s | ~21% faster |

### Changes

#### 1. Compiled Binary Caching

Added a caching mechanism to avoid unnecessary recompilation of the same parsers:

- Introduced `IntegrationHelper.compiled_parsers` hash to track compiled binaries
- Cache key includes both parser name and lrama command arguments
- Only recompiles when the parser hasn't been built or the binary doesn't exist
- Particularly effective for parsers used multiple times:
  - `after_shift`: used 2 times
  - `destructors`: used 4 times

#### 2. Optimized Compiler Flags

Changed GCC compilation flags to prioritize compilation speed over runtime performance:

- Changed from `-ggdb3` to `-g` (minimal debug info)
- Added `-O0` flag (no optimization)
- These changes are appropriate for integration tests since we only care about correctness, not runtime performance

#### 3. Memory Cleanup

Added `after(:all)` hook to clear the compiled parsers cache, preventing memory bloat during test runs.

Author: ydah

spec/lrama/integration_spec.rb

@@ -6,6 +6,12 @@
 
 RSpec.describe "integration" do
   module IntegrationHelper
+    @compiled_parsers = {}
+
+    class << self
+      attr_accessor :compiled_parsers
+    end
+
     def exec_command(command)
       `#{command}`
       raise "#{command} failed." unless $?.success?
@@ -35,9 +41,14 @@ def test_parser(parser_name, input, expected, expect_success: true, lrama_comman
         debug = true
       end
 
-      Lrama::Command.new(%W[-H#{parser_h_path} -o#{parser_c_path}] + lrama_command_args + %W[#{grammar_file_path}]).run
-      exec_command("flex --header-file=#{lexer_h_path} -o #{lexer_c_path} #{lexer_file_path}")
-      exec_command("#{compiler} -Wall -ggdb3 -I#{tmpdir} #{parser_c_path} #{lexer_c_path} -o #{obj_path}")
+      cache_key = "#{parser_name}_#{lrama_command_args.join('_')}"
+
+      unless IntegrationHelper.compiled_parsers[cache_key] && File.exist?(obj_path)
+        Lrama::Command.new(%W[-H#{parser_h_path} -o#{parser_c_path}] + lrama_command_args + %W[#{grammar_file_path}]).run
+        exec_command("flex --header-file=#{lexer_h_path} -o #{lexer_c_path} #{lexer_file_path}")
+        exec_command("#{compiler} -Wall -O0 -g -I#{tmpdir} #{parser_c_path} #{lexer_c_path} -o #{obj_path}")
+        IntegrationHelper.compiled_parsers[cache_key] = true
+      end
 
       out = err = status = nil
 
@@ -58,12 +69,17 @@ def test_parser(parser_name, input, expected, expect_success: true, lrama_comman
 
     def generate_object(grammar_file_path, c_path, obj_path, command_args: [])
       Lrama::Command.new(%W[-d -o #{c_path}] + command_args + %W[#{grammar_file_path}]).run
-      exec_command("#{compiler} -Wall #{c_path} -o #{obj_path}")
+      exec_command("#{compiler} -Wall -O0 #{c_path} -o #{obj_path}")
     end
   end
 
   include IntegrationHelper
 
+  # Clear cache after all tests to save memory
+  after(:all) do
+    IntegrationHelper.compiled_parsers.clear
+  end
+
   describe "calculator" do
     it "returns 9 for '(1+2)*3'" do
       test_parser("calculator", "( 1 + 2 ) * 3", "=> 9")