Strip internal triple backticks from extracted code blocks to resolve parsing errors

[toadlyBroodle]

• What: Updated extract_code_from_text in src/smolagents/utils.py to remove any occurrences of triple backticks from within extracted code blocks.
• Why: Prevents persistent code block parsing errors caused by stray ``` inside model outputs.
• How: Cleans each matched code block via match.replace("```", "").strip() before joining.
• Scope: Limited to code extraction logic; no API or behavior changes outside parsing.
• Impact/Risk: Low; only affects handling of malformed code blocks.