Add POETRY_VIRTUALENVS_IN_PROJECT environment variable support

[Copilot]

The extension ignores POETRY_VIRTUALENVS_IN_PROJECT, so .venv directories in Poetry projects aren't correctly identified as in-project Poetry environments. The PET server already handles this env var, but the extension's own classification logic in nativeToPythonEnv didn't account for it.

Changes

• src/managers/poetry/poetryUtils.ts: Added isPoetryVirtualenvsInProject() that checks process.env.POETRY_VIRTUALENVS_IN_PROJECT for "1" or "true" (case-insensitive), mirroring the PET server logic in pet-poetry/src/env_variables.rs
• nativeToPythonEnv: When the env var is set and the environment has a project association (info.project), skip the global virtualenvs directory check — these are in-project envs, not global ones

export function isPoetryVirtualenvsInProject(): boolean {
    const value = process.env.POETRY_VIRTUALENVS_IN_PROJECT;
    if (value === undefined) {
        return false;
    }
    return value === '1' || value.toLowerCase() === 'true';
}

• src/test/managers/poetry/poetryUtils.unit.test.ts: 9 unit tests covering truthy/falsy values and case sensitivity

Original prompt

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This section details on the original issue you should resolve

<issue_title>Poetry: Missing support for POETRY_VIRTUALENVS_IN_PROJECT environment variable</issue_title>
<issue_description>## Problem

The extension does not honor the POETRY_VIRTUALENVS_IN_PROJECT environment variable when determining whether a .venv directory in a project should be treated as a Poetry environment.

Expected Behavior

When POETRY_VIRTUALENVS_IN_PROJECT=true (or 1) is set, Poetry creates virtualenvs in the project's .venv directory. The extension should recognize these as Poetry environments.

Current Behavior

The extension doesn't check this environment variable, so .venv directories in Poetry projects may not be correctly identified as Poetry environments.

PET Server Reference

The PET server properly handles this in pet-poetry/src/env_variables.rs:

poetry_virtualenvs_in_project: env
    .get_env_var("POETRY_VIRTUALENVS_IN_PROJECT".to_string())
    .map(|v| v == "1" || v.to_lowercase() == "true"),

And in pet-poetry/src/environment_locations.rs:

fn should_use_local_venv_as_poetry_env(
    global: &Option<Config>,
    local: &Option<Config>,
    env: &EnvVariables,
) -> bool {
    // Given preference to env variable.
    if let Some(poetry_virtualenvs_in_project) = env.poetry_virtualenvs_in_project {
        return poetry_virtualenvs_in_project;
    }
    // ...
}

Suggested Fix

Add support in poetryUtils.ts to:

1. Check process.env.POETRY_VIRTUALENVS_IN_PROJECT
2. Consider .venv as a Poetry env when this is set and the parent has pyproject.toml with [tool.poetry]

Related

This is similar to how poetry.toml local config with virtualenvs.in-project = true should work.

Affected File

src/managers/poetry/poetryUtils.ts</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Poetry: Missing support for POETRY_VIRTUALENVS_IN_PROJECT environment variable #1183

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