gh-143423: Fix free-threaded build detection in sampling profiler

[DCchoudhury15]

Description

This PR corrects a logic error in Lib/profiling/sampling/sample.py where _FREE_THREADED_BUILD was incorrectly evaluated as True on Windows non-free-threaded builds when Py_GIL_DISABLED was explicitly set to 0.

The detection has been updated from an is not None check to a bool() cast, which correctly handles:

• 1 -> True
• 0 -> False
• None -> False (standard builds)

Additionally, I have updated _new_unwinder to properly handle the all_threads vs only_active_thread parameters based on the detected build type.

Tests

• Verified reproduction by checking that _FREE_THREADED_BUILD returns False when sysconfig.get_config_var("Py_GIL_DISABLED") is 0.
• Ran the official test suite: ./python -m test test_profiling (Passed).

• Issue: gh-143423

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[DCchoudhury15]

@pablogsal up for review

[vstinner]

cc @pablogsal