Languages: Add additional runtimes

[cuevaio]

Description

Expand exec0 to support additional programming languages beyond JavaScript/TypeScript.

New Runtimes

• Python
• Go (performance-focused)
• Rust

Tasks per Language

• Set up Lambda runtime/layer
• Implement execution handler
• Wire into logging pipeline
• Wire into billing pipeline
• Support all machine types where applicable
• Add language-specific error handling
• Create example snippets
• Update API to accept language parameter

Acceptance Criteria

• Each language executes correctly on Lambda
• All languages use the same logging/billing infrastructure
• Machine types work across all languages
• API properly routes to correct runtime
• Documentation updated for each language