Constantly changing deps folder makes sam build caching useless

## Problem

No way to leverage sam build cache when debugging since dependencies are always in a new folder and downloaded.

## Steps to reproduce the issue

1. Make a SAM Python application with a Lambda.
2. Set up launch.json to debug with --cache.
3. Run debugging, get message: "[info] Manifest file is changed (new hash: ) or dependency folder (.aws-sam\deps\) is missing for (), downloading dependencies and copying/building source".
4. Complete debug run.
5. Run debugging again with zero edits, get message: "2025-07-03 17:36:49.524 [info] Manifest file is changed (new hash: ) or dependency folder (.aws-sam\deps\) is missing for (), downloading dependencies and copying/building source".
6. Since deps folder guid is new, dependencies are redownloaded, function is rebuilt.

## Expected behavior

Debugging happens immediately with existing code rather than a 5 minute wait.

## System details (run `AWS: About` and/or `Amazon Q: About`)

- OS: Windows 10
- Visual Studio Code version: 1.95.0
- AWS Toolkit version: 3.68.0
- Amazon Q version: N/A

Start by tracing how the SAM Python debug flow handles launch.json with --cache and creates the .aws-sam/deps/ folder. Compare the dependency-folder path across two unchanged debug runs and identify where the new identifier is generated. Done means a repeated debug run reuses the existing dependencies instead of downloading and rebuilding them.

Written by the indexing model from the issue text.