Support for inline environment variables

[jritsema]

Many MCP servers have required envvars. It appears that they are not supported in the mcp tools command? For example:

$ mcp tools AWS_REGION=us-east-1 FASTMCP_LOG_LEVEL=ERROR uvx awslabs.aws-api-mcp-server@latest
Error: failed to start stdio transport: failed to start command: exec: "AWS_REGION=us-east-1": executable file not found in $PATH
Example: mcp tools npx -y @modelcontextprotocol/server-filesystem ~