Preserve exception chain in morsel_to_cookie max-age conversion

[tboy1337]

Summary

This PR improves exception handling in the morsel_to_cookie function by preserving the original ValueError when a max-age conversion fails, following Python's exception chaining best practices.

Changes Made

• Modified src/requests/cookies.py:

  • Updated the exception handling in morsel_to_cookie() to use raise ... from exc syntax
  • This preserves the original ValueError as the __cause__ attribute when raising a TypeError

• Added test in tests/test_requests.py:

  • New test test_max_age_exception_chaining() to verify exception chaining behavior
  • Validates that the TypeError is raised with the correct message
  • Confirms the original ValueError is preserved in the exception chain
  • Verifies the ValueError message contains "invalid literal for int()"

Motivation

Previously, when an invalid max-age value was provided, the original ValueError from int() conversion was lost, making debugging more difficult. By using proper exception chaining (raise ... from exc), developers can now:

• See the complete exception traceback
• Understand both the high-level error (invalid max-age) and the low-level cause (ValueError from int conversion)
• Leverage Python's exception chaining features for better debugging and logging

Testing

The new test ensures that:

1. The appropriate TypeError is still raised for invalid max-age values
2. The error message remains descriptive and helpful
3. The original ValueError is accessible via the __cause__ attribute
4. The complete exception chain is preserved for debugging purposes

Impact

• No breaking changes - The external behavior remains the same (still raises TypeError)
• Better debugging - Developers get more context when errors occur
• Best practices - Follows PEP 3134 for explicit exception chaining

[tboy1337]

I should add that this issue was found because of I think (I'm not 100% sure because everything was also typed according to mypy rules in the commit) pylint in #7054, if it was pylint that found this issue and it is a legitimate issue then it makes a strong case for the project to start using it imo.