Improve StrictMock guidance for undefined callables

[KSAGlory]

What:

Improves UndefinedAttribute messages for callable attributes on templated StrictMock objects. Synchronous callables now point to testslide.mock_callable(), while coroutine functions point to testslide.mock_async_callable().

Fixes #128

Why:

The existing message only says that the attribute must be set. For template methods, that misses TestSlide's dedicated callable-mocking APIs, which provide call validation and expectations.

How:

StrictMock.__getattr__ inspects the matching template attribute and appends a targeted tip. The tests cover synchronous and asynchronous instance, static, and class methods while preserving the existing message for non-callable attributes.

Risks:

Low. The exception type and existing message prefix are unchanged. Only callable attributes receive one additional guidance line.

Test results:

• Passed all six focused synchronous and asynchronous callable guidance cases.
• Passed the existing non-callable undefined-attribute cases.
• Passed the full StrictMock test file except the pre-existing Python 3.13-incompatible subclass context.
• Ruff formatting passes.
• Ruff reports no warnings beyond those already present on main.
• git diff --check passes.

Testing limitation:

The complete StrictMock test file cannot pass locally on Python 3.13 because the existing subclass setup rejects Python 3.13's __firstlineno__ attribute as unsupported. This failure occurs on untouched main and is unrelated to this change. The repository CI uses Python 3.10.

Checklist:

• Added tests, if you've added code that should be tested
• Updated the documentation, if you've changed APIs - N/A, no API change
• Ensured the test suite passes - Focused and compatible tests pass; full local execution is blocked by the pre-existing Python 3.13 issue described above
• Made sure your code lints - No new lint warnings
• Completed the Contributor License Agreement ("CLA")