[Feature Request] Track and report usage of virtualenvs across project directories

[aksajja]

Description

pyenv-virtualenv keeps track of all virtual environments created using pyenv virtualenv, but does not track where those environments are used (i.e., which directories contain .python-version files referencing them).

This feature would improve environment management by logging usage context and allowing users to query where virtualenvs are active.

Problem

• No way to map virtualenvs to the directories that use them
• Makes it hard to clean up, audit, or understand which projects rely on which environments
• Users have to manually grep for .python-version files to infer usage

Proposed Feature

Introduce optional usage tracking for virtualenvs:

• When a virtualenv is activated (via pyenv activate, or a .python-version triggers it), log an entry with:
  • Timestamp
  • Virtualenv name
  • Path to the directory where it was used

Provide a new CLI command:

• pyenv virtualenv usage — List all usage across virtualenvs
• pyenv virtualenv usage <env-name> — Show where a specific env is used

Logging should be opt-in via an environment variable or config, such as:

export PYENV_VIRTUALENV_LOG_USAGE=1