feat: Prepare for code modularization and cleanup

- Archive old documentation and test files to `docs/archive/` and `local_tests/`.
- Remove various temporary and old files from the project root.
- Add `nekocode-rust` analysis tool and its output files (`nekocode/`, `.nekocode_sessions/`, `analysis.json`).
- Minor updates to `apps/chip8_nyash/chip8_emulator.nyash` and `local_tests` files.

This commit cleans up the repository and sets the stage for further code modularization efforts, particularly in the `src/interpreter` and `src/parser` modules, based on recent analysis.

local_tests/test_arithmetic.nyash

@@ -0,0 +1,7 @@
+// 算術演算テスト
+print(2 + 3)
+print(10 - 4) 
+print(5 * 3)
+print(15 / 3)
+print("Hello" + "World")
+print("Test" * 3)