Hash Virtual Environment Cache Based on Actual Package Versions in `PythonVirtualEnvOperator`

### Description

Update the `PythonVirtualEnvOperator` to hash the virtual environment cache based on the actual versions of the installed packages rather than just the checksum of the requirements. This change would ensure that the cache reflects the true state of the environment, avoiding issues with packages tagged as **"latest"** or other dynamic versioning.

### Use case/motivation

Currently, when using the `PythonVirtualEnvOperator`, if dependencies in the requirements use tags like **"latest"**, the checksum used for caching remains unchanged even if the package versions are updated. This can lead to situations where outdated versions of packages are used from the cache, causing potential inconsistencies and issues in workflows. By hashing the cache based on the actual versions of installed packages, the virtual environment would be refreshed appropriately whenever package versions change, ensuring that the most current versions are used.

### Related issues

_No response_

### Are you willing to submit a PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

Start by locating the PythonVirtualEnvOperator and its virtual environment cache checksum logic. Trace how requirements and installed package versions are currently represented, then define completion as cache keys changing when dynamically resolved package versions change, with coverage for that behavior.

Written by the indexing model from the issue text.