test: cover two-sided clamp boundaries - #429

Description

This PR adds test coverage for existing, previously untested two-sided range clamping and boundary conditions in humanize.clamp().

Covered Behaviour

• Supplying both floor and ceil simultaneously.
• Values within the range return the formatted value without a token.
• Values below floor are clamped correctly when ceil is also provided.
• Values above ceil are clamped correctly when floor is also provided.
• Values exactly equal to floor or ceil remain un-tokenized.

Changes

• Added 5 parameterized test cases to tests/test_number.py.
• No production code was changed.
• No configuration or infrastructure was changed.

Verification

• Full test suite before changes: 746 passed, 110 skipped
• New clamp tests: 16 passed
• Full test suite after reverting the intentional regression: 751 passed, 110 skipped
• Intentionally changing value > ceil to value >= ceil caused the new boundary test to fail, confirming that the test detects the regression.