Use default environment even when env is provided

[maxguru]

Fixed issue #326 - MCP client with npx not working when env parameter of StdioServerParameters is set

Motivation and Context

See issue #326
Discarding the output of get_default_environment() when server.env has additional variables doesn't make sense. A reasonable assumption is that setting env variables adds to what was there otherwise.

How Has This Been Tested?

I tested it and it fixed the issue for me.

Breaking Changes

If somebody relied on setting the env parameter to clear default environment variables then they would need to change their code.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• [?] Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

None

[dsp-ant]

Can you please fix the formatting issue? You should be able to run uv run ruff format