Thread-safety / free-threaded fixes with tests

[greateggsgreg]

Recent commits declared the module free-thread-compatible (Py_MOD_GIL_NOT_USED, PR #119) and rewrote pytsk3's own error storage to be thread-local (PR #118). This PR addresses other thread safety and security issues surfaced during testing.

I introduced fine-grained locking (per-instance, not module-wide), so on free-threaded Python pytsk3 calls genuinely run in parallel. Stress workload: 32 threads x 2000 iters x 6 reads = 384,000 ops on a shared File:

Build	Time	Speedup
Python 3.14 GIL	1.55 s	baseline
Python 3.11 GIL	1.57 s	~same as 3.14 GIL
Python 3.14t free-threaded	0.18 s	~9×

Tests include:

• Concurrent ops: independent and shared Img_Info/FS_Info/File/Volume_Info reads, opens, and iterations.
• Parent keepalive: every child path (Directory.iternext, File.iternext, FS_Info.open*, File.as_directory, Volume_Info.iternext, borrowed-struct getters) survives parent drop + GC.
• Close-vs-read race: Img_Info.close from one thread while readers are mid-flight produces a clean IOError, never a crash.
• Iterator cursor: 4 threads sharing one Directory iterator consume exactly baseline entries — no duplicates, no skips.
• Recursive walk stress + GC under load: 8 threads × 20 iters × full tree walk with concurrent gc.collect() produces identical entry counts.
• Subinterpreter import: validates tsk_init's std::call_once across interpreters
• Security: Tests for regressions of security-relevant issues that include an out-of-bounds read and NULL deref issues

Finally - I added Python 3.14 free-threaded build targets for all platforms which also have tests run against them.

#121

[greateggsgreg]

Looks like ubuntu repos are having connectivity issues. Run a rebuild on the same code and it should be fine.

[joachimmetz]

per https://status.canonical.com/

Canonical and Ubuntu Status
Canonical’s web infrastructure is under a sustained, cross-border attack and we are working to address it. We will provide more information in our official channels as soon as we are able to.