Recommended packaging setup for SAM stacks

I'm currently working on an project that uses multiple AWS SAM stacks.
Some include one or more lambda's and various resources using Python 3.12.

We want the code to be easily testable and decoupled from eachother. Also, we want to keep our deployed lambda functions small, we don't want to deploy the whole project.
Per stack, I was thinking the underneath structure.

```bash
# lambda one code
~/project_sam_stack_one/template.yaml
~/project_sam_stack_one/src/lambda_one/__init__.py
~/project_sam_stack_one/src/lambda_one/module_one.py
~/project_sam_stack_one/src/lambda_one/module_one.py
~/project_sam_stack_one/src/lambda_one/somedir/__init__.py
~/project_sam_stack_one/src/lambda_one/somedir/module_nested.py

# lambda two code
~/project_sam_stack_one/src/lambda_two/__init__.py
~/project_sam_stack_one/src/lambda_two/module_one.py
~/project_sam_stack_one/src/lambda_two/module_one.py
~/project_sam_stack_one/src/lambda_two/somedir/__init__.py
~/project_sam_stack_one/src/lambda_two/somedir/module_nested.py

# shared library
~/project_sam_stack_one/src/shared_code/__init__.py
~/project_sam_stack_one/src/shared_code/postgres.py

# testing
~/project_sam_stack_one/tests/...

# packaging to make the project installable and easy to test
~/project_sam_stack_one/pyprojerct.toml
```

When then deploying the lamdbas, to ensure we don'at deploy the full project, we set the `CodeUri` to each of the lambdas:

`~/project_sam_stack_one/src/lambda_two/`

This means, from within the runtime of the lambda, the `PYTHONPATH` will be set to the `CodeUri`. This breaks.

The option I can think of: doubling the directory structure to simulate the package being installedModify the `PYTHONPATH` and double your directory structure to
For this approach, the lambda packages are doubled. This is inspired by [this article, doubling the directory structure](https://xebia.com/blog/python-and-relative-imports-in-aws-lambda-functions/).

```bash
# lambda one code
~/project_sam_stack_one/template.yaml
~/project_sam_stack_one/src/lambda_one/__init__.py
~/project_sam_stack_one/src/lambda_one/module_one.py
~/project_sam_stack_one/src/lambda_one/module_one.py
~/project_sam_stack_one/src/lambda_one/somedir/__init__.py
~/project_sam_stack_one/src/lambda_one/somedir/module_nested.py

# lambda two code
~/project_sam_stack_one/src/lambda_two/__init__.py
~/project_sam_stack_one/src/lambda_two/module_one.py
~/project_sam_stack_one/src/lambda_two/module_one.py
~/project_sam_stack_one/src/lambda_two/somedir/__init__.py
~/project_sam_stack_one/src/lambda_two/somedir/module_nested.py

# shared library
~/project_sam_stack_one/src/shared_code/__init__.py
~/project_sam_stack_one/src/shared_code/postgres.py

# testing
~/project_sam_stack_one/tests/...

# packaging to make the project installable and easy to test
~/project_sam_stack_one/pyprojerct.toml
```

For local development, this requires the `PYTHONPATH` to be modified, but feels weird with importing.

## Questions
- Aside from the list above, are there any othere recommended approaches?
- Can we implement something in the application to ease this process?