Restructure Python package to follow best practices (#22)

Reorganize the Python emulator to follow Python Packaging Authority (PyPA)
guidelines and the "src layout" pattern. This makes the package structure
more professional, standard, and maintainable.

Changes:
- Move Python modules from src/ to src/host_emulator/
- Update package configuration in pyproject.toml with explicit package location
- Update all imports from "from src import" to "from host_emulator import"
- Maintain proper src layout to prevent accidental import of development version

New structure:
  py/host-emulator/
  ├── src/
  │   └── host_emulator/    ← Proper package name (underscores for Python)
  │       ├── __init__.py
  │       ├── common.py
  │       ├── emulator.py
  │       ├── i2c.py
  │       ├── pin.py
  │       └── uart.py
  ├── tests/
  └── pyproject.toml

This structure follows:
- PEP 420 (Implicit Namespace Packages)
- PyPA packaging best practices
- Src layout pattern for proper isolation

All 29 tests continue to pass.

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

Co-authored-by: Claude <noreply@anthropic.com>

Author: nehalkpatel

py/host-emulator/pyproject.toml

@@ -4,6 +4,7 @@ version = "0.1.0"
 description = ""
 authors = ["Nehal Patel <hereisnehal@gmail.com>"]
 readme = "README.md"
+packages = [{include = "host_emulator", from = "src"}]
 
 [tool.poetry.dependencies]
 python = "^3.11"

py/host-emulator/src/__init__.py …t-emulator/src/host_emulator/__init__.pypy/host-emulator/src/__init__.py renamed to py/host-emulator/src/host_emulator/__init__.py py/host-emulator/src/__init__.py renamed to py/host-emulator/src/host_emulator/__init__.py

@@ -1,10 +1,9 @@
 import pathlib
 import subprocess
 
+from host_emulator import DeviceEmulator
 from pytest import fixture
 
-from src import DeviceEmulator
-
 
 def pytest_addoption(parser):
     parser.addoption(

py/host-emulator/src/common.py …ost-emulator/src/host_emulator/common.pypy/host-emulator/src/common.py renamed to py/host-emulator/src/host_emulator/common.py py/host-emulator/src/common.py renamed to py/host-emulator/src/host_emulator/common.py

@@ -1,6 +1,6 @@
 from time import sleep
 
-from src import Pin
+from host_emulator import Pin
 
 pin_stats = {}