refactor: reorganize project into src/ structure

- Move all scripts (p2pk, p2pkh, p2sh, p2wpkh, p2tr) into src/
- Rename main.py to __main__.py to allow running with `python .`
- Update script paths in __main__.py
- Translate README to English and update launch instructions
- Add __pycache__, *.pyc, *.json to .gitignore

.gitignore

@@ -2,4 +2,12 @@
 venv/
 .venv/
 env/
-ENV/
+ENV/
+
+# Python cache
+__pycache__/
+*.pyc
+*.pyo
+
+# File JSON generati dal programma
+*.json