fix: preserve tool argument whitespace

[he-yufeng]

Summary

• preserve non-sentinel string arguments exactly in get_function_call
• keep the existing string-to-None/True/False normalization based on trimmed comparison text
• add regression coverage for leading/trailing whitespace and whitespace-only strings

Closes #7871

To verify

• python -m pytest libs/agno/tests/unit/utils/test_functions.py -q
• python -m ruff check libs/agno/agno/utils/functions.py libs/agno/tests/unit/utils/test_functions.py
• python -m py_compile libs/agno/agno/utils/functions.py libs/agno/tests/unit/utils/test_functions.py
• git diff --check

[github-actions]

PR Triage

Issue assigned to someone else: This PR references an issue that is already assigned:

• Issue [Bug] get_function_call strips intentional whitespace from string arguments, breaking tools that rely on newlines #7871 is assigned to @harshsinha03

Please confirm with the assignee or a maintainer in the issue comments before proceeding.

---

This PR has been automatically closed. The linked issue is already assigned to someone else. If you believe your contribution is valuable, please comment on the original issue explaining your approach and why it might be preferred. A maintainer can reopen this PR if appropriate.

[harshsinha03]

LGTM! Thanks for contributing and appreciate you using Agno!